Question

Could the League of Nations act against the aggression?

Answer 1

In theory yes they could, practically speaking maybe not. One of the basic ideas of the League of Nations was Collective Security. The flaws in the system were shown over time.

Explanation:

The League could certainly act, in theory, against an aggressor but its constitution required an unanimous decision on action so any no vote was a veto. It also depended on the Great Powers to provide an armed force to act upon its decisions and if they were not inclined to (regardless of treaty commitments) then nothing happened.

https://en.wikipedia.org/wiki/Collective_security#Collective_security_in_the_League_of_Nations