forming an alliance; conclusion of a treaty of alliance
Formal term used in political or diplomatic contexts for the act of entering into an alliance or treaty.
The two countries agreed to form a military alliance.
The signing ceremony for the treaty will be held next month.
Compound of 締 (tighten, conclude) and 盟 (alliance). The exact historical derivation is uncertain, but the kanji combination directly conveys the meaning of concluding an alliance.