The Dark Continent.
The American imperative to dominate Europe.
Across the past four centuries of American settlement, European affairs have enmeshed America and Americans in armed conflict more than any other regional source excluding the territory of America itself. The list is extensive.
There were the prodigious number of pre-independence conflicts, ranging from small-scale Anglo-French and Anglo-Spanish skirmishes, to the array of major European wars with American adjunct theaters. The War of the League of Augsburg ravaged Europe from Ireland to the Rhineland throughout the 1690s, and also a far-flung series of American local theaters from Hudson Bay to the Hudson River. The War of the Spanish Succession dragged in the Americas through the early 1700s on battlefields from Florida to Newfoundland. Spain and England managed to fight an all-American war, including direct campaigning pitting Florida versus Georgia, beginning in the late 1730s. The War of the Austrian Succession through the 1740s visited destruction upon modern-day Nova Scotia and wiped out settlement north of Albany. The Seven Years War through the 1750s and early 1760s consumed the entirety of Canada, Quebec, and the British colonies north of Virginia.
Those are just the big ones. Then there was the American War of Independence, which concluded in 1783 and, the Founders hoped, would insulate the new American republic from the predations of the Old World.
America was back at war with European powers — or their proxies — within two years, as the British stoked and supplied the opposing tribes in the Northwest Indian War, which dragged on through 1795. Three years after that, America waged a two-year defensive naval war against revolutionary France. In the following decade, America was compelled into a second defensive naval war, this time against Britain. That slow burn of a conflict finally erupted into full warfare in 1812, concluding three years later in an uncertain fashion. The rest of that decade featured intermittent American raids into Spanish Florida, ending with Spain yielding the territory entirely.