How to get Ally to help you in battle when Overwhelmed ?

[SP2244]

My enemy has almost 15 stacks now (3x clusters of 5 stacks), not sure how that is possible. they sent 5 stacks to take my city , held off as my forces arrived.... but then the 5 stacks headed back for home as saw my backdoor approach to their capital with another force. So then 5 more stacks were generated out of thin air. I am at turn like 65 or so, even with 4 cities I can not general that volume of stacks so fast ... they obviously spawned out of thin air (AI cheated)... The movement of these stacks is not far from their main city, so clear all coming from same place and same type of unit family (all are rock throw from their home city).

I am overlord of one faction and trying to call them in for support - but see no button or method to get them to send troops. How do you call ally into battle for you.....

Clearly these stacks must be an AI triggered response to something I did .... but 3 clear clusters of 5 each moving a separate full teams. With that force they could likely take over the whole board - which is really unfair since clearly was spammed out of thin air as I was close to main enemy city.... and they have 1 other city to support them (played with 3 enemies, killed 1, Overlord of the other, and now trying to finish this one off - but impossible now).