With the ending of the bloody Thirty Years War, in which one third of Europe's population died, the Peace of Westphalia was signed which established the concept of sovereignty or the authority of a state to govern itself or another state. Additionally, this concept remains the foundation of contemporary international politics and provides the backbone for state interaction.

As the sixteenth century drew to a close, the nature of religious conflict in Western Europe experienced a dramatic shift. The Treaty of Augsburg (1555) was successful in resolving the disputes between the Catholic Church and Lutheranism. Specifically, it was the Treaty’s provision which allowed the leader of each regional/national territory to independently decide the dominant religion of their domain that enforced this new peace. While the Treaty had officially made Lutheranism a protected religion, it offered no such security to Calvinism. Naturally, Calvinists found this unfair and intolerable and so the focus of religious conflict shifted, as Calvinists arrayed themselves in fierce, vocal (and sometimes physical) opposition to the Catholic Church. This struggle, Calvinists against Catholics, was especially strong in Scotland, France, the Netherlands, and England.

The late sixteenth century was a time of great religious turmoil in France. The French government and monarchy were staunchly Catholic but the country also had a growing population of Protestants, who were known as Huguenots. Religious conflict was deeply intertwined with political conflict, especially because many French nobles who had been excluded from positions of power by King Francis II found Protestantism’s advocacy of decentralized control to be perfectly suitable to their political ambitions. The French monarchy officially began an Inquisition against Huguenots in 1540. In response, aristocratic Protestants, such as the prince of Conde and Admiral Coligny, began to create their own Protestant militias, which were well-armed and lived inside fortified towns. This intermarriage between politics and religion created a dangerous climate in the country, one which could erupt at any moment. The final push into outright conflict came right after the King’s death; because his heir, Charles IX, was too young to rule, his mother, Catherine de Medici, became Queen Regent. Although she was a devout Catholic, Catherine didn’t want to see her nation torn apart by religious infighting, but she was unable to restrain her fellow Catholic nobles, many of whom had also assembled their own militias. The conflict came to a head in March 1562, when the Catholic duke of Guise and his militia burst into a Protestant church in Champagne and massacred many of the worshippers. The brutality of the attack, especially the duke’s invasion of a church and his acts of violence within a sacred space, convinced the Huguenots that they couldn’t tolerate any future aggression and the French civil war of religion soon began.

The Saint Bartholomew’s Day Massacre is the most infamous moment in the entire course of the French religious war between the Catholics and Huguenots. The Massacre occurred on August 24th, 1572, after religious conflict had been ravaging the nation off and on for the last decade. Queen Catherine de Medici had heard rumors of a planned Huguenot attack against her, as retaliation for her role in the attempted assassination of Admiral Coligny, one of the Huguenot’s main military leaders. Driven to desperation, Catherine decided that she and her Catholic forces, led by the duke of Guise, had to strike back before the Huguenot plot could occur, and so she persuaded her son, King Charles IX, to agree to a pre-emptive assault. On August 24th (aka Saint Bartholomew’s Day according to the Catholic Church calendar), Catholic forces murdered Coligny and three thousand other Huguenots in the streets of Paris. This first massacre was followed by a series of coordinated attacks all across the country, during which Catholic soldiers killed twenty thousand more Huguenots. The Massacre did not have the effect that Catherine and the other Catholic leaders had planned, however. Instead of convincing the Huguenots to back down and sue for peace, it convinced nearly every Huguenot that they had to intensify their military campaign against the French monarchy and the Catholic militias. The French religious war became a literal fight to the death, with the Huguenots more determined than ever to fight for their survival.

Sixteenth-century France’s brutal religious war between Catholics and Huguenots was finally ended by the Edict of Nantes. Passed on April 13th, 1598, the Edict of Nantes was the brainchild of King Henry IV (aka Henry of Navarre), who came to power after the assassination of King Henry III. Despite his Huguenot faith, Henry IV was a true “politique” who believed that French social and political unity should be prioritized. After decades of warfare, with numerous atrocities committed by both sides, most French people were war-weary and desperate for peace. Additionally, Henry IV enjoyed widespread public popularity, from Catholics and Huguenots alike, which certainly helped his advocacy for a ceasefire. When Henry IV assumed the throne on July 25th, 1593, he made a dramatic announcement, in which he stated that he was converting to Catholicism because it was the religion of the majority of his subjects. Perhaps surprisingly to outsiders, most of France deeply supported Henry IV’s conversion, which he publically billed as the first step towards peace. A few years later, Henry IV made the final step: his issuance of the Edict of Nantes. The Edict put an end to any further religious warfare and also granted Huguenots many religious freedoms, including the right to worship freely, to gather freely, and to remain living inside their fortified towns. This peace would last but sadly, Henry IV would not – he was assassinated by a disgruntled Catholic in 1610.

For many centuries, Spain, a staunchly Catholic and firmly monarchial country, had been one of Europe’s biggest power players. Spain’s defeat and removal of the Moors (aka Muslim peoples who lived across the Mediterranean, African, and Middle Eastern regions) from Spanish territory had convinced the royal family that only by enforcing strict religious conformity could they maintain tight political control. At first, under the leadership of King Phillip II, this effort was quite successful – in 1580, the Spanish Army crushed revolts in neighboring Portugal, giving Philip II control over Portugal’s rich trading empire. Looking to consolidate this success, Philip II next looked to the Netherlands, a region over which he exercised hereditary control, thanks to his Habsburg heritage. But the people of the Netherlands weren’t used to being closely ruled (past Spanish monarchs had largely ignored them) and they certainly weren’t all willing to convert to Catholicism. In fact, many of the wealthiest cities in the region, such as Antwerp, were mostly Calvinist in denomination. Soon enough, a bitter religious rebellion against Philip II broke out in the Netherlands, spearheaded by the Count of Egmont and Prince William of Orange. Despite numerous and ruthless defeats on the battlefield, Prince William and his fellow rebels continued to fiercely resist Spanish governance, off and on, from the late 1560s all the way until 1609, when an exhausted Spain was finally forced to cede defeat and grant the Netherlands its independence.

While it is true that the various provinces of the Netherlands were united in their opposition to Spanish rule, they were not all united in their religious outlook. Many of the northern provinces (such as Holland and Utrecht) were almost entirely Calvinist, while the southern areas were much more Catholic-dominated. Still, the two sides managed to put aside their religious differences in favor of achieving political freedom – in 1577, every province came together to form the Union of Brussels. This Union was entirely committed to uniting the full force of Dutch military might against Spain and for almost two years, this plan worked brilliantly. However, the Union fell apart in 1579, as the Spanish army gained a stronghold in a few southern provinces, a scary reality which in turn made many Dutch Catholics begin to question the true motives of their Calvinist countrymen. In response, the southern provinces declared that they were breaking off the Union of Brussels and forming the Union of Arras instead, to wage their own fight against Spain. The northerners, led by Prince William of Orange, banded together in the new Union of Utrecht.

Throughout the late 1560s, a serious of disastrous events and troubling occurrences pushed the governments of Spain and England ever closer to war. Spain was intensely annoyed when Queen Elizabeth I of England gave monetary support to the Dutch rebels who were fighting against Spanish control of their region. Meanwhile, Elizabeth I was quite suspicious of the presence of the Spanish Army in the Netherlands, a locale which she felt was too close for comfort to the English coastline. Additionally, several English pirates/privateers (including Sir Francis Drake) began attacking and raiding Spanish ships, which Elizabeth I claimed to know nothing about (much to King Phillip II of Spain’s disbelief). The final tipping point came when Elizabeth I executed her cousin and closest rival for the throne, Mary, Queen of Scots, on February 18th, 1587 for treason. Elizabeth I had been presented with proof that Mary had been involved in a plot to assassinate Elizabeth and place Mary on the English throne instead. This scheme was especially treacherous because the Spanish Ambassador to England, who was a friend of Mary’s, was caught attempting to seek his government’s help in carrying out the planned murder. After the execution, both sides knew that this conflict had become far too big to ignore. With the approval of Pope Sixtus V, Spanish King Phillip II assembled his forces and began to prepare his infamous navy, the Armada, to invade England.

When war first broke out between Spain and England in 1587, following English Queen Elizabeth I’s execution of Mary, Queen of Scots, many onlookers would most likely have seen Spain as the clearly inevitable victor. However, this was not at all the case. Despite King Phillip II of Spain’s attempts to muster his army and navy swiftly so that he could invade England, the English forces were able to strike first. In 1587, Sir Francis Drake, a famous privateer, led the English navy on a series of devastating assaults on the main Spanish port of Cadiz and various spots along the coast of Portugal. Drake’s attack on Cadiz ended up destroying part of the Spanish Armada (aka the navy), forcing Spain to postpone its invasion until repairs could be made. Finally, the Armada was ready and on May 30th, 1587, it sailed off for England. But in a shocking turn of events, the English navy completely shattered the world-famous Armada; about one-third of the Armada’s ships were ruined, sunk, or otherwise lost. This defeat crippled Spain, both militarily and politically. In the eyes of much of Western Europe, the once all-mighty Armada had been defeated and this meant that Spain was now vulnerable. The country was never quite able to recover the prestige and power it once had wielded. England and France took advantage of this power vacuum and moved to fill it, not only within Europe but also in the New World, where they gradually took over Spain’s colonies.

The Thirty Years’ War can be rather difficult to understand at first, especially because by the time it ended in 1648, nearly every country and/or region in Western Europe had become somehow involved. It is important to keep in mind that, despite all the fighting over pieces of territory and alliances, the primary cause of the war was actually religious fervor and hatred. The Peace of Augsburg (1555) had established an uneasy truce but many rulers refused to respect the right of other leaders to peacefully decide the religious orientation of their own regions. Through political and economic pressure, many monarchs attempted to change the dominant religion of other nations, as Ferdinand II did when he became Holy Roman Emperor in 1619. Such schemes were especially frequent within the scattered German territories (no united country of Germany yet existed). The Germanic region, because of its perfect geographic position, was a rich highway of trade for the entire continent and all the separate German territories were used to governing themselves without outside interference. However, the Germanic region was torn apart by internal conflict between nearly equally strong Lutheran and Calvinist factions. The situation was further intensified when Frederick III became the Elector Palatine (aka the ruler) of the Palatinate, a tiny region near modern-day Luxembourg. Frederick III was a devout Calvinist who wanted to spread his faith and so he formed a Protestant military and made alliances with England, France, and the Netherlands against Catholic Spain. The Holy Roman Empire (which was seen as the main stronghold of Catholicism) didn’t want to leave its Catholic ally, Spain, vulnerable and so it rushed to the country’s aid, which turned up the temperature even further. Seeing this, the German territories also began to take sides, and perhaps the richest region, Bavaria, which was mostly Catholic, allied itself with Spain. The duke of Bavaria, Maximilian I, formed a Catholic military defense league to oppose Frederick III’s Protestant league. A confrontation was now basically unstoppable.