As I understand them,
- American Revolution - "No Taxation Without Representation" and resulted in documents foundational to American liberalism, like the Bill of Rights and Declaration. Politically and philosophically motivated, not expansionist.
- American Civil War - A war of secession, with abolitionism as a root issue. There were economic factors, like the North's industrialization, but to say that this war is imperialist is to legitimize the Confederacy's claim to preserve the institution of American slavery.
- WWI - America supported Britain and France but was isolationist, until the sinking of the Lusitania. America entered the war to defend trading partners, but again, that doesn't make this imperialist.
- WWII - Again, America was initially isolationist until a decisive moment (this time, Pearl Harbor). Again, this was more diplomatically motivated than a surplus of capital or land-grabbingly expansionism.
It wasn't until the post-WWII era of the Cold War that America shifted gears from a habit of isolationism to global interventionism, and began a long line of imperialist atrocities.
I'm only bringing these wars up because they're the ones I'm familiar with - I'm sure there are plenty of examples of wars across the globe, even in more modern eras, that Western Liberals wouldn't call imperialist.