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,

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.