Positional Theme #2 a-pawn vs b5 -- Part1!
Black often expands on the queenside with ...a6 and ...b5 in a wide variety of openings, from the Queen's Gambit Declined to Sicilian and King's Indian Defenses. But this comes with a risk: White can train more firepower on b5 than Black- and that makes a2-a4! dangerous. Here we see a4 allowing White to gain control over c4.