That makes it seem like a security guarantee would risk deeper US involvement, as eventually happened with Korea, Vietnam, and Iraq I.
It seems to me that your logic would make the Iraq War quite defensible. Iraq had already invaded Kuwait. We had already guaranteed Kuwait’s security, so we would’ve had to send troops if Saddam invaded again. So if the CIA was correct that Saddam was rearming, there was a logic to deposing him now and resolving the situation on terms favorable to us, instead of reactively getting involved at a future date. Without the benefit of hindsight—knowing Saddam didn’t have WMDs—it seems like the only basis for opposing the Iraq War under your logic would have been to quibble about how much of an affirmative step Saddam had to take before our obligation to put boots on the ground kicked in.
You're right, it really depends on what the security guarantees are, how they're stated, and whether they're credible.
As an example of a case that has worked, the mutual security guarantees within NATO have prevented WWIII so far. (knock on wood)
Obviously, we should be trying to go for something more like the latter.
Alternately, of course, no security guarantees, and both sides continue to fight.
China is already closely watching how the west responds to Ukraine, with potential implications for Taiwan. This increases the likelihood that American security commitments/requirements will eventually be tested more directly.
It seems to me that your logic would make the Iraq War quite defensible. Iraq had already invaded Kuwait. We had already guaranteed Kuwait’s security, so we would’ve had to send troops if Saddam invaded again. So if the CIA was correct that Saddam was rearming, there was a logic to deposing him now and resolving the situation on terms favorable to us, instead of reactively getting involved at a future date. Without the benefit of hindsight—knowing Saddam didn’t have WMDs—it seems like the only basis for opposing the Iraq War under your logic would have been to quibble about how much of an affirmative step Saddam had to take before our obligation to put boots on the ground kicked in.