Other forms: balances of power
When countries around the world have approximately the same amount of military strength, it's called a balance of power.
In international relations, balance of power is just one theory about how to maintain stability and reduce conflicts between nations. The idea is basically that smaller countries can join alliances, combining their military power so that it's more or less equivalent to what big, powerful nations possess. Ultimately, the goal is to keep any one country from becoming dominant over all the others.