I would agree with this. These wars have largely been advocated and presented as ideological wars (i.e. "making the world safe for democracy," "defending freedom," etc.), not actual homeland defense.
These are PR slogans, to sell the war to the people. In your examples, the US rushed in at the last moment so it could claim a share of the spoils.
The US has been involved in dozens of wars, annexations and puppet regimes since then, not for any righteous principle or to benefit the people on either side, but to benefit United Fruit Company, Raytheon, Exxon-Mobile, or Halliburton. In the US, the military fights for corporations; for the 1%, not for 'the country', the people or any abstract notion like freedom.
I suppose in this day and age, crippling the enemy's infrastructure and offensive capacity could be adequately done by air bombardment or missile barrages from the sea (or through the use of drones). Unless we actually need to conquer and control a territory (and why would we want to), do we really need boots on the ground with armies of conscripts?
Interesting point. I hadn't really broken it down by methodologies, but since you brought it up, it seems like aerial bombardment would be the 'easiest', least disruptive to the homeland, most dehumanizing, and most harmful to civilians and infrastructure. Victims characterize it as cowardly.
These days conquering, controlling and exploiting territory is largely done by proxy. We threaten, we trick them into debt, we create or support anti-government militias, we install puppets willing to exploit their own people in exchange for our maintaining them in power, &c. Boots on the ground are a last resort.
None of this, of course, has anything to do with promoting democracy or with any benefit to The People in general.
Confessions of an Economic Hit Man - Wikipedia
Boots on the ground risks public disapproval, but may be necessary to 'mop up' after an actual attack, till puppets can be installed.
The "military, industrial complex" requires continual conflict to sell and create demand for its products; to maintain the thousands of military related jobs and the communities they support.
I wouldn't compare it to slavery. Slavery implies a permanent state of affairs, and it is also generational. If you're a slave, then your children would automatically be slaves as well. A slave would not be a citizen, so a slave would have no rights whatsoever, such as the right to vote, right to marry, right to own property - rights which a conscript would still have. Conscripts would still get a salary for their service, while slaves do not typically get paid.
However, the biggest difference is that slavery is a capitalist invention, designed for the profit and benefit of private sector entities. It does not benefit the state as a whole, as exemplified by how terrifically outmatched the Confederacy was against the Union. The irony in the result was that the very cause the South was fighting for was what doomed them to defeat.
There are degrees of "slavery." It's a catch-all term, denoting varying degrees of inequality; unfair, hierarchical relationships, contractual inequality or servitude. &c.