It's not easy to establish a clear line in history between the time when American democracy belonged to citizens and when it was lost, but wars give us starting point.
The first wars were fought over ideas. There was the Revolutionary War in the 18th century and then in the 19th century, the Civil War "preserved the union' and ended slavery.
In the 20th century came the wars for national imperialism. First, Teddy Roosevelt's wars in the Philippines and Cuba, then WWII which more or less accidentally resulted in imperial expansion.
After 1945, the U.S. was very good at waging war but no longer so good at winning, so we kept practicing. Wars waged against Korea and Vietnam failed to accomplish anything but massive destruction on somebody else's land, ratchet up the hate index for the U.S., and give the Pentagon an excuse to exercise its military muscles and escalate its budget.
Increasingly, especially since the implosion of the U.S.S.R. in 1989, the U.S. military has been used as a tool to interfere in the politics of smaller and weaker nations, to intimidate and harass, to make the world safe for corporations, which is also known euphemistically as "making the world safe for democracy' and "protecting American interests.'
The U.S. has been the only unchallenged superpower since the collapse of the Soviet Union. Relieved of the need to protect the world from "the communist threat', citizens expected the defense budget, larger for many decades than the military budgets of the rest of the world combined, to finally yield to common sense. Americans anticipated a peace dividend in spending that reflected the irrelevance of the military sink hole and left room to support the economy, education, and social programs.