Machines saved Empire from extinction when they were caught between LH and Cyber and lost all their worlds very early on.
When Empire took worlds totally surrounded by us, instead of wiping them out again when we were at peace with Dynasty and had no other borders, we let them take those 3 worlds and signed a treaty.
Also, all your infrastructure on Warsaw is warp jammed, but war with us would mean we can bomb it, so nobody wants that.