What is the London System opening?
You can not always force it because for example
1. D4 nf6 2. Bf4 c5 3. Nf3?! cxd4 and white is forced to take with the queen or play a gambit with c3 because if white plays 4. Nxd4?? After 4. E5! 5. Bxe5 there is Qa5+ winning a piece
So you have to play depending on the position
Sometimes it’s better to play c4 than c3 in the london