bribes
("hello france, have this massive stack of €€ so you can beat up England, in return, cancel your deal with targetstan plx ")
threats
("hello nobodystan-who-is-allied-to-targetstand-and-bbb-and-friends, please cancel your alliance or I will curbstomp you in 4 seconds flat ")
simple trading
("hello france, wouldnt you rather be allied with bigbadME instead of silly little targetstan, I promise to help vs England, and I have lotsa €€")
spies
(ye olde horses-head-in-bed usually gets the point across, or oh I dunno plant evidence of betrayal)
Combination
("hello sir please help me push this cart. In return carrots and mah spies wont beat you with sticks today")