I don't understand what black should play for after either 1...e5 or 1...c5. I would appreciate if someone could provide me some ideas or which games/players/articles/videos I could have a look at. I am particularly interested in the Four knights variation, because I can't understand what seems to be the main line:
The point of 4. g3 Bb4 is because by playing g3, White intends to establish a fianchettoed bishop on g2, which indirectly exerts dominance on e4. Black then plays Bb4 in order to prevent White from successfully playing e4 immediately, since the knight on c3 can no longer protect e4 securely, as it is threatened by Bxc3, bxc3, Nxe4; allowing Black to win a free pawn.
In 6. O-O e4, White gets his king safe, obviously. The point of e4 is for Black to gain space in the center, as well as to chase away the knight on f3, which will eventually result in a weakness on h2. The downside to this move is that White will be attacking the pawn twice, while Black only once, when the knight is relocated. The next move is likely to be 7. Ng5 Re8.
I would appreciate if someone could provide me some ideas or which games/players/articles/videos I could have a look at. I am particularly interested in the Four knights variation, because I can't understand what seems to be the main line:
1.c4 e5 2.Nc3 Nf6 3.Nf3 Nc6 4.g3 Bb4 {Why?} 5.Bg2 O-O 6. O-O e4 {Why?}