Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nc6/3. Bc4

= Vienna Game =

3. Bc4
This sequence of opening moves is, objectively speaking, not an effective way for white to maintain any advantage. White's development of these two pieces is considered unharmonious. In particular, the bishop on c4 is prone to being attacked. However in practice, black may respond with the 'copycat variation' 3... Bc5, and after 4.Qg4, white has a definite advantage. From there, white can play with a plan of f4 if there is no knight on f3 blocking the f-pawn. If for example black plays 3... Nf6 4.d3 Na5, then white can consider 5.Nge2, which creates imbalances in the position and reserves the possibility of f4 later.

Theory table
.

1. e4 e5 2.Nc3 Nc6 3.Bc4