The Spanish-American War was likewise begun under suspicious circumstances, but it was the first fueled mainly by the press.
The US also engaged in pointless wars like WWI and unjust wars like the Indian Wars following the Civil War.
"War is a racket" sounds interesting, so I'd be curious to read the arguments. Maybe my interpretation is wrong or incomplete! I do think there was a significant shift from wars being perpetrated by elected officials seeking political ends to wars being largely planned and executed by the MID (and the press), with the elected leaders dragged along like the tail wagging a dog.
Did we?
After independence, we spent about a century engaged in war with native tribes until they'd effectively been wiped out. The conflicts spanned from Florida to California, Texas to the Dakotas.
We invaded and annexed half of Mexico. We attempted to invade Canada in the War of 1812. We fought in North Africa not long after securing our independence and would do so multiple times.
We were pioneers in industrial total war which we practiced upon ourselves in the Civil War.
We won Cuba, Puerto Rico and the Philippines from Spain in a war that had much flimsier causes than WMDs in Iraq and lacked any semblance of a noble goal.
The Department of Defense came after WWII, and while we've had our fair share of at best misguided wars since then, it's not a recent development.
That's not to say the name isn't Orwellian in nature.
I made another comment conceding the point about the the Mexican-American and Spanish-American wars, which were fraudulent albeit separated by several decades.
Nevertheless, the thought of the US Government unilaterally dropping bombs or executing a raid on sovereign foreign countries like we have done in Iraq or Pakistan would have been seen as outrageous before the DoD days, notwithstanding that the United States is the preeminent economic and military power today. But I think that fits in with OP's point: the incompetence is a feature of giant, hegemonic power, not a bug.
To your latter point, the US became significantly more bellicose after the War Department became the Defense Department (merged with the Navy Department). This coincided with escalating dishonesty about the wars the US was making. The Korean War was at the time a "police action." The casus belli for full commitment in the Vietnam War was the fraudulent Gulf of Tonkin incident. And then, of course, who could forget the the invisible WMDs in Iraq?