The tradition of natural law ethics spans from at least the Stoics through the Middle Ages and beyond. It has earlier resonances in Aristotle as well. Its greatest development occurred in the Middle Ages into early modernity. While the Treatise on Law in the Summa theologiae of Thomas Aquinas is an important text in the natural law tradition, he is actually not the correct answer for this question. He did not write much (if anything) on international law. That really was not a problem in the Latin Middle Ages.

Instead, it is to the Dutch jurist and political philosopher Hugo Grotius that we must turn for such matters. Writing in the midst of many international conflicts in Europe, Grotius penned works like De Jure Belli ac Pacis (On the Law of War and Peace) as well as an important tract on the rights of nations on international waters. He undertook to discuss what rights pertain to people naturally as well as how these are related to the rights of nations. His work was not utterly unique, but it was an important touchpoint for later writers on these matters.

It was George Berkeley who stated esse est percipi. In his Three Dialogues between Hylas and Philonous and A Treatise Concerning the Principles of Human Knowledge, he lays out a scathing critique of John Locke. Berkeley truly believed that Locke's theory of knowledge and metaphysics would lead to skepticism. He tried to overcome this by saying that all of reality is made up of ideas. That is things themselves are ideas and we know those very ideas. This required him to undertake a number of interesting discussions which, although quite strange, present a very interesting set of philosophical musings.

The "Hegelian dialectic" is often rendered as Thesis-Antithesis-Synthesis, meaning any statement can be opposed by an opposite idea, and the clash of the two ideas will create a better philosophical statement. Hegel preferred the terms "abstract," "negative," and "concrete," which better explained the ideas' relationship. Hegel's dialectic was widely influential; it was used by thinkers like Karl Marx and argued against by philosophers such as Søren Kierkegaard and Friedrich Nietzsche.

Immanuel Kant was the most important philosopher of the late eighteenth century. His 1783 work The Critique of Pure Reason established his view that rationality and thought could sufficiently form the basis of morality. In particular, Kant stressed that a prirori, or given as true, knowlegde is all synthetic.

The 1776 work The Wealth of Nations proved a highly influential work on the theory and philosophy behind capitalism. Its author, Adam Smith, introduced the concept of the invisible hand, the notion that a free market will regulate itself. The book set a course for economic theory and philosophy at the start of the Industrial Revolution.

The Pensées were published posthumously, after their author, Blaise Pascal, had died from a long illness in 1662. The jottings and musings on religion and philosophy were beginning to be compiled into some form by Pascal, but it is unclear how close he came to a finished version. The famous concept known as "Pascal's Wager," which asserts a proposition for belief in God, is found in The Pensées.

Jean-Jacques Rousseau's 1762 book Emile, or on Education is a rumination on the proper way to educate a child, which focuses on a boy named Emile who follows Rousseau's ideal model. Rousseau advocates allowing a child to discover himself so that the innate natural goodness of man will not be corrupted by society. Rousseau's attacks on the Catholic church saw his book banned at publication, but Emile helped provide a basis for education in Revolutionary France.

John Locke's Two Treatises of Government, published after England's Glorious Revolution of 1689, attempts to defend a system government based on natural rights and contract theory. Locke's work argued against absolute monarchy and for a form of representation. The work proved highly influential, with many of its ideas being foundational for the Founding Fathers of the United States of America.

You might be tempted into picking one of the medieval authors as an answer for this question (i.e. Thomas Aquinas or Duns Scotus), but this is not the case. Instead, the correct answer is the Dutch philosopher Baruch Spinoza (1632-1677). Spinoza built upon the ideas of René Descartes but was also very well schooled in the scholastic philosophy of his day, which had roots in many medieval discussions including that of the great Jewish Philosopher, Jurist, and Theologian Moses Maimonides. He was also influenced by Hellenistic philosophers, especially the Stoics.

In his Ethics, Spinoza uses certain, shall we say, less than perfect scholastic formulations of the notion of substance. This leads him to say that God can be the only substance. Everything else is just a mode or attribute of this one substance. This is a kind of extreme pantheism—meaning that God is everything. Some actually accused Spinoza of being an atheist—precisely because he equated God with the world.

The Federalist Papers were a series of public essays written variously by John Jay, Alexander Hamilton, and James Madison, all as an attempt to help gain support for the ratification of the US Constitution. The papers dealt with a variety of issues about the new federal government itself, the status of the citizens in that government, and the rights of the states in that federal union. During the time of the drafting of the Constitution, Jefferson was abroad in France as a minister plenipotentiary. He most certainly could not be an author of these papers! (He was, however, a close friend of Madison and did, in fact, help Madison craft a reading list to prepare for thinking about the many matters pertaining to the Constitution's drafting.)