We cooperated TODAY (今日= KYOU)
There's THREE 'strong' radicals, so you can say:
Three strong people cooperating have the strength of ten people working alone.
協 (cooperate) + 力 (strong)
= 協力 (cooperation)
妥 (compromise) + 協 (cooperate)
= 妥協 (compromise)
協 (cooperate) + 会 (big meeting)
= 協会 (union)
a society or association - but usually used about labor unions.