General Idea:
Every so often an event would occur impacting either everyone globally, a pair of alliance members or one player.
Benefits:
This would give a bit more variance to games, reward responding quickly and correctly to unexpected events, help break deadlocks and create emergent gameplay narratives.
Potential downsides:
I could see this annoying some people due to the randomness of the events possibly making it so a game that was going well suddenly shifts for the worse
Possible ways to mitigate issues:
Have events only occur in some number of games, say every 4th game in the lobby rotation.
Event examples:
Time of Chaos (global) - and all alliances are dissolved without penalty, you can choose to reform them or use this as an opportunity to backstab without penalty.
Calls for War (personal) - you get a buff for attacking someone attacking an ally or who has amassed too much power too quickly.
Tariffs (alliance) - trade income is reduced for X seconds
(On mobile, sorry for the lack of formatting, might fix it later if people seem to like this.