Pledge
Pact
noun, verbal noun
An alliance promise is one that's made with a pledge or pact. Imagine making an alliance with someone, pledging your support.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
トーフグと盟約を結びたいんです。
We want to form a pact with Tofugu.