So I've started a game a few times now, and every time I'm either locked against the coast or a peninsula, with the AI quickly building a city and outposts blockading me in. This in and of it's self is frustrating, but it's always a militaristic AI so they love to skirmish. In my last game I tried being friendly, trade routes and such but they just keep attacking my units, when I air a grievance they ignore it. 

Then they start getting pissy because they want my regions and start demanding them whenever I offer up a new treaty like "non-agression pact" even though the regions aren't necessarily on their borders. I say no and they just get more pissy about this.

I was going to get down to some war but the mechanics of population really hampered that idea. I like the mechanics but I don't understand them. It seems like to mount a big enough force to take on this empire I'd need to go down to almost starvation by taking away workers. I also don't quite understand the war support meter. They were at one point 74/100 war support but their bar looked pretty empty, it was quite far to the left, which in my mind is low support. 

So I'm stuck between a rock and a hard place. I have no where else to expand too, the city blocking me in is really upset demanding my territories constantly, and anytime my units get anywhere near theirs they skirmish me. 

And this is all on normal difficulties, the 4th difficulty option. I love the game but I don't understand why this keeps happening and what to do.

TL;DR: AI keeps blocking me in and demanding my land, I don't know how to manage population and a warforce early on, help. 

Growing population is extremely important if you want to build military units. (note : you can disband surviving units afterward to gain back the population)

Being able to win most fights while evenly matched is also important. Try to only fight when you have the terrain advantage (fortifications and/or high ground)

Note : I just lost my whole army before turn 100 when I tried to attack the 1st AI on unknown terrain. He had twice as much units and they were more advanced. So I guess recon is also quite important :)