The Gulf War took place from 1990 to 1991 and was triggered by Iraq's invasion of Kuwait. Iraq invaded Kuwait in August 1990 and the US, with its allies, launched Operation Desert Storm as a response, starting a war. Iraq's actions were condemned by the international communities, and economic sanctions were placed on the country. Led by the US into Saudi Arabia, many countries joined the Coalition and began aerial and ground attacks. 

The other options for this question are incorrect because they are not accurate for the time period, geographically incorrect, or irrelevant in this particular outbreak of war. 

The Chinese Civil War was interrupted by the invasion of Japanese forces in the 1930s. Although the two sides were hardly cooperative with one another, they both turned to meet the larger threat presented by Japanese occupation. The civil war was suspended from 1937 until 1946. Much of Mao’s popularity in China emerged from his organized resistance against the Japanese forces.

The British had a pact with the Belgians to protect them in the event of a major conflict. Once the Germans began blazing a path to France through the small country, Britain's hand was forced and their entrance into the first major global conflict became unavoidable. 

The Serbian assassin, Gavrilo Princip, was merely 19 years old when he set the events of World War I into motion. Commonly referred to as an "accidental assassin," Princip only happened to cross paths with the Archduke's car as he was leaving a pub. Acting quickly, he shot both the Archduke and his wife, Sophie. He then attempted to commit suicide by taking a cyanide tablet; however, the tablet was ineffective and Princip would live to see the trickle-down effect of his actions.

By Armistice Day in 1919, 100 countries had become embroiled in the conflict known as World War I. Not only did the 'Great War' result in millions of casualties for these nations, but it also brought the world into the modern era.

Though Iraq had a horrific human rights record and extreme tensions with its Middle Eastern neighbors, and had declared that it would use chemical weapons on Israel in case of military invasion, none of these was the immediate cause of the war. Instead, Iraq’s invasion of Kuwait in August 1990 and subsequent control over its oil fields merited an international response. 

Japanese troops blew up part of the South Manchurian Railway in September 1931, and accused China of orchestrating the incident. Japan used this incident as a pretext to invade Manchuria, which it had gained complete control over by 1932. 

After the invasion, the Chinese turned to the international community for help, and the League of Nations attempted to bring Japan to the negotiation table. By 1932, Japan had ignored international entreaties, withdrawn from the League and established a puppet state of Manchuko. 

After the formation of the Israeli state by the United Nations from lands claimed by the Palestinians, there were decades of conflict. Israelis cracked down hard on Palestinian demonstrations, and also confiscated the land owned by Palestinians. A combination of Israeli land confiscations and the growing Palestinian population created bad conditions for Palestinians, including rising unemployment levels and poor living conditions.

After the Oslo Accords in 1995, Israel committed to withdrawal from some contested areas and to respect the Palestinian right to certain areas of land, but the bloodshed did not stop in subsequent years, and both sides were deeply disappointed with the process. In 2000, Israeli opposition leader Ariel Sharon visited the Temple Mount, which includes the very holy Al Aqsa mosque. This sparked Palestinian riots and quickly turned into widespread demonstrations and violence.