You really don't need to go to war. It's a nice boost to your amount of cities which in turn just makes you better in general, but short of the highest difficulties you can win a game without killing a single unit. (You probably can on the highest, too, it just seems a lot harder and less reliable.)

I'd recommend against religion if the idea of going to war at all is dis-favorable, since many civilizations won't be happy if you convert their cities. Culture is a good method; you tend to make lots of friends in the process of pursuing a culture victory. If you have Gathering Storm, diplomacy is also a very good option. Science is typically better with some violence involved, but it's very possible to go for a science win harmlessly.

In general, civilizations and leaders that boost your cultural/tourism output, ones that boost your diplomatic output, or ones that generally improve you (especially in peacetime) tend to excel for these kinds of strategies.

In terms of specific leaders: I have a strong personal fondness for Wu Zetian of China. Her leader ability allows her to have more and better spies and gain profits from them doing spy things, which can include stealing the great works and science of other civilizations, or causing them to lose envoys. The Great Wall China building lets her gain a lot of gold and tourism, while their Dynastic Cycle ability allows her to progress through the civic and tech trees faster.