Diplomatic for me. probably because i dont go for it.
That's actually the easyist to achieve if you do go after it.
1. Follow the standard science is King for every victory condition tactics.
2. After finishing your first tree but before you are allowed into Rationalism, open Patronage to allow construction of the Forbidden Palace wonder for 2 extra votes.
3. Standard first spy in your capital and all future ones initially to protect key city state allies.
4. Construct NIA somewhere just for that extra spy.
5. Adopt Freedom, following the completion of Rationalism then pick Freedom tenents to advance to level 3 as quickly as possible and pick the one giving influence every turn with city states you have a trade route. (About that time reroute trade routes to city states)
6. About mid way into Modern era, divert from the standard tech play in favor of a strict beeline to Globalism.
7. Propose World Ideology of Freedom for two extra votes.
8. Ensure that you have enough votes to be the leader of the UN when crossing into information era for the extra votes from being the host.
9. About the time you discover Globalism turn all spies into diplomats to get 1 extra vote per diplomat.
10. At this point buy city states where needed / use your military to liberate city states the AI conquered.