United States non-interventionism primarily refers to the foreign policy that was eventually applied by the United States between the late 18th century and the first half of the 20th century whereby it sought to avoid alliances with other nations in order to prevent itself from being drawn into wars that were not related to the direct territorial self-defense of the United States. Neutrality and non-interventionism found support among elite and popular opinion in the United States, which varied depending on the international context and the country's interests. At times, the degree and nature of this policy was better known as isolationism, such as the interwar period.
Due to the start of the Cold War in the aftermath of World War II and the rise of the United States as a global superpower, its traditional foreign policy turned towards American imperialism with diplomatic and military interventionism, engaging or somehow intervening in virtually any overseas armed conflict ever since, and concluding multiple bilateral and regional military alliances, chiefly the North Atlantic Treaty Organization. Non-interventionist policies have had continued support from some Americans even after World War II, mostly regarding specific armed conflicts like the Vietnam and Korean wars or the more recent Syrian Civil War.
Background
Robert Walpole, Britain's first Whig Prime Minister, proclaimed in 1723: "My politics are to keep free from all engagements as long as we possibly can." He emphasized economic advantage and rejected the idea of intervening in European affairs to maintain a balance of power. Walpole's position was known to Americans. However, during the American Revolution, the Second Continental Congress debated about forming an alliance with France. It rejected non-interventionism when it was apparent that the American Revolutionary War could be won in no other manner than a military alliance with France, which Benjamin Franklin successfully negotiated in 1778.
After Britain and France went to war in 1792, George Washington declared neutrality, with unanimous support of his cabinet, after deciding that the treaty with France of 1778 did not apply. Washington's Farewell Address of 1796 explicitly announced the policy of American non-interventionism: The great rule of conduct for us, in regard to foreign nations, is in extending our commercial relations, to have with them as little political connection as possible. Europe has a set of primary interests, which to us have none, or a very remote relation. Hence she must be engaged in frequent controversies the causes of which are essentially foreign to our concerns. Hence, therefore, it must be unwise in us to implicate ourselves, by artificial ties, in the ordinary vicissitudes of her politics, or the ordinary combinations and collisions of her friendships or enmities.
No entangling alliances (19th century)
President Thomas Jefferson extended Washington's ideas about foreign policy in his March 4, 1801 inaugural address. Jefferson said that one of the "essential principles of our government" is that of "peace, commerce, and honest friendship with all nations, entangling alliances with none." He also stated that "Commerce with all nations, alliance with none", should be the motto of the United States. Extending at times into isolationism, both Jefferson and Madison also practiced the boycotting of belligerent nations with the Embargo Act of 1807.
In 1823, President James Monroe articulated what would come to be known as the Monroe Doctrine, which some have interpreted as non-interventionist in intent: "In the wars of the European powers, in matters relating to themselves, we have never taken part, nor does it comport with our policy, so to do. It is only when our rights are invaded, or seriously menaced that we resent injuries, or make preparations for our defense." It was applied to Hawaii in 1842 in support of eventual annexation there, and to support U.S. expansion on the North American continent.
After Tsar Alexander II put down the 1863 January Uprising in Poland, French Emperor Napoleon III asked the United States to "join in a protest to the Tsar." Secretary of State William H. Seward declined, "defending 'our policy of non-intervention—straight, absolute, and peculiar as it may seem to other nations,'" and insisted that "[t]he American people must be content to recommend the cause of human progress by the wisdom with which they should exercise the powers of self-government, forbearing at all times, and in every way, from foreign alliances, intervention, and interference."