Pledge
Pact
noun, verbal noun
めいやく
条件 （じょうけん） Condition, Conditions, Terms, Requirements
条約 （じょうやく） Treaty, Pact, Agreement
契約 （けいやく） Contract, Agreement
盟約 （めいやく） Pledge, Pact
誓約 （せいやく） Vow, Pledge, Oath, Covenant
約款 （やっかん） Agreement, Stipulation, Article, Clause
An alliance 盟 promise 約 is a Pact 盟約
He Pledged to board the Mayflower めい in exchange for a yak やく in the new world.
He made めい his yak やく Pledge allegiance to him.