joining (an association, agreement, etc.)...

Japanese Confederation of Labor (1964-1987) (abbr), Dōmei

to swear, to vow, to take an oath...

league, federation, union

league, federation, union

leader (of an alliance), leading power

sworn friend

oath, pledge, pact...

alliance, aimag, league...

treaty of alliance

ally, allied powers

association formed to carry out an objective

blood pledge, oath signed in blood

forming an alliance, conclusion of a treaty of alliance

concluding an alliance, making a pledge

to form an alliance

non-alignment, nonalignment

trial by hot water, putting a person's hand in boiling water to determine their guilt or innocence (with the belief that the innocent would not be scalded)

capitulation, surrender, treaty signed under coercion

member nation, member state, signatory

participant, member

participating store, participating merchant, member store...

allied armies

allied nation, ally

Hanseatic League

Delian League (the Athenian empire)

Arab League

Confederation of the Rhine (1806-1813)

military alliance

boycott, buyer's strike