seen off, diffuse, not susceptible

[Klpno]

Hello, everybody.
I'd like to ask a question about the meaning of 'seen off', 'diffuse' and 'not susceptible' in the following passage:

By the last quarter of the twentieth century Europe was an important regional economic power but no longer a major world power. The American economic superiority of the early and mid-twentieth century was also lost in the second half of the century as Europe recovered from its civil wars, more countries industrialized and Japan became just as wealthy. America's global military power had seen off the limited challenge by the Soviet Union but it provided little real gain in power in circumstances where security problems were increasingly diffuse and not susceptible to military solutions.

I think that 'had seen off' means 'had experienced', 'diffuse' means 'widespread and indistinct' and 'not susceptible' means 'that cannot be solved by'.

Do I understand the meanings correctly?

[Mister Micawber]

.
Seen off = watched depart; here, it means that US power remained intact while Soviet power came and went.

Diffuse = what you said.

Not susceptible = what you said.
.
_________________
Native English teacher at Mister Micawber's

[Klpno]

Thank you very much, Mister Micawber!!!