Wherever there are states, there are treaties. Since ancient times, treaties have been a crucial tool of statecraft and diplomacy. As treaties are agreements between various states, often concluded at the end of a conflict, they profoundly reshape boundaries, economies, alliances and international relations. Here are five of the most important treaties in history.

Treaty of Tordesillas (1494)

The Treaty of Tordesillas, between Portugal and Spain (technically its component Kingdom of Castile), was negotiated by the Papacy and divided newly discovered lands outside of Europe between the two countries along a line of longitude through what is now eastern Brazil.

As a result, Spanish exploration and colonization mostly focused on the Americas, leading to Spanish control over much of Central and South America; the still undiscovered Brazil fell to Portugal. Portugal was able to explore east, and under Vasco da Gama in 1498, it managed to establish that it was possible to sail from Europe to India.

Initially, the treaty was to Portugal’s advantage, as it grew rich off of the trade route between Europe and Asia. However, in the long run, Portugal was edged out of this trade by England and Holland. In terms of controlling land, it was much more difficult for tiny Portugal to seize and hold territory where organized states existed in Asia. Spain, on the other hand, acquired a huge and populous empire in Latin America, and later discovered enormous mineral wealth there.

Ultimately, of course, other powers chose to ignore the treaty, which excluded them, including England, the Netherlands and France.

The Peace of Westphalia (1648)

The Peace of Westphalia consisted of two related treaties, the Treaty of Münster and the Treaty of Osnabrück, signed at the end of the Thirty Years’ War, which was generally between Catholic and Protestant states, although countries like France played both sides for cynical gain. Although the Peace of Westphalia only originally impacted Western and Central Europe, it eventually had global consequences.

This was because it established some of the most important principles of the international system. The key characteristics of the nation-state were laid out in the treaties signed at the Peace of Westphalia. The treaties established the idea of territorial sovereignty, with each state solely responsible for law and order, taxes and control over the populations in their territories. Additionally, the right of every state to order its own internal religious and political arrangements was recognized. These are now considered global norms.

The Treaty of Paris (1783)

The Treaty of Paris (1783), which is the oldest treaty signed by the United States still in effect, ended the American Revolution and established the United States—for that reason alone, it is one of the most consequential treaties in world history. The Treaty of Paris didn’t just establish the United States; it did so on highly favorable terms.

The American negotiating team, led by John Jay, Benjamin Franklin and John Adams played their hand astoundingly well. America’s allies, France and Spain, did not want the United States to make a separate peace; however, as fighting continued to rage in the Caribbean and Gibraltar, this is exactly what the Americans sought, as they felt they would get a better deal by directly dealing with London. The French had hoped that America would be a small and weak state between the Atlantic and Appalachians, with the British keeping the lands north of the Ohio River and the Spanish controlling a buffer state to the south. Instead, the British decided that a strong and economically successful America was in their interests and against French interests and were convinced to give the new state all the land up to the Mississippi river as well as fishing rights in Canada. This enabled the United States to later expand westward and become a major continental power.

The Congress of Vienna (1814–15)

The Congress of Vienna occurred at the end of the Napoleonic Wars and dramatically reshaped Europe. Several treaties were signed at the Congress, the most important of which was the 1814 Treaty of Paris (there are a lot of “Treaties of Paris”).

The Congress of Vienna was especially noteworthy because of how successful it was. While some later historians have criticized it as being “reactionary,” it prevented the outbreak of a major European war for a hundred years. How did it accomplish this?

First, all parties, including defeated France, were part of the negotiations. This was due to the informal format of the Congress, which allowed various parties, often led by brilliant diplomats such as Talleyrand (France) and Metternich (Austria) to sit down and hash out their positions, until a compromise was reached. While this did not make everyone happy, it ensured that nobody was totally unhappy and involved convoluted horse-trading. For example, Sweden lost Finland to Russia, but gained Norway from Denmark. Denmark, in turn, gained Swedish Pomerania and the Duchy of Lauenburg from Hanover; it gave the first to Prussia and kept the second. In compensation Hanover was given East Frisia from Prussia.

Second, the Congress and the resulting treaties limited the level of punitiveness imposed on the losing parties. France lost the territory acquired by Napoleon but kept its prewar boundaries; it was more often than not treated by the other powers as a fellow victim of Napoleon. Countries that sided with France, like Saxony were allowed to retain their independence, despite calls to the contrary. Unlike the aftermath of World War I, no attempts were made to abolish entire countries or change their internal political arrangements. All this contributed to enormous stability. The only unfortunate thing was that, because of all the horse-trading at the conference, an independent Poland was not reestablished.

Treaty of Versailles (1919)

The Treaty of Versailles was signed between the Western allies and Germany at the end of World War I. The manner in which it was handled stood in stark contrast with the inclusive way in which post-Napoleonic Europe was organized—terms were dictated, not negotiated. In addition to the Treaty of Versailles, Austria, Hungary, Bulgaria and the remnant of the Ottoman Empire also signed misconceived treaties.

Germany, of course, was given the short end of the stick, and was punished with the loss of territory and crippling reparations, largely at the urging of a vengeful France. While this was a bad idea, if the allies were going to go down this path, they should have gone ever further and broken up Germany, rather than let Europe’s most populous nation fester in anger.

President Woodrow Wilson’s Fourteen Points also lead to the creation of various new, small, weak nation-states which could hardly defend themselves in the long run against predatory powers like the Soviet Union and Germany. Interference in the internal political structures of defeated powers like Germany also created the conditions for trouble, and ultimately lead to World War II.

The related treaties of Sèvres and Lausanne divvied up the Ottoman Empire, with unpleasant consequences for the Middle East: Armenians and Kurds lost out, and most of the Arabs found themselves under French and British colonial rule in artificial states like Syria and Iraq, the consequences of which are abundantly evident today.

Akhilesh Pillalamarri is an international relations analyst, editor and writer, who contributes to the Diplomat and the National Interest. He received his Master of Arts in Security Studies from the Edmund A. Walsh School of Foreign Service at Georgetown University, where he concentrated in international security. You can follow him at his Twitter handle @akhipill.

Image: Political situation after the Congress of Vienna in June 1815. Wikimedia Commons/Creative Commons/Alexander Altenhof