I'm trying to learn the London System

I'm trying to learn the London System. It looks very powerful, but when I tried to play it, I noticed that in the tutorials I watched, Black was always casling the king side, which never happened in my games.

What do I do when this happens? What if my opponents castle queen side?

You sound like you are memorizing and not actually understanding. When you study an opening, is all you do try to memorize reams of lines? If so, you are doing it all wrong.

You also cannot just randomly pick an opening, say "I am going to learn X" and expect to just have it all hit you instantly. You actually have to be able to explain in words what the purpose of each move is for BOTH SIDES (not just White's or Black's). Otherwise, you don't actually understand the opening and you are wasting your time.

Often, opponents are not going to play optimally. Case in point. I had a game over the board maybe 6 or 7 years ago. I was Black, and the game started 1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Qb6 5.Ne2.

If all I did was memorize lines, I would be as lost as I would be if you were up a queen. But I actually understand the French, and understood that this weakens the support of e5, and if f4, then the moment White castles he will have problems on d4 with the pin.

I shifted my attack from d4 to e5, had a completely winning position by move 18 and won in under 30 moves.

Compare that to another opening, the Grunfeld Defense. Let's take the Seville Variation. Sure, I could spew out 13 moves of theory - 1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.e4 Nxc3 6.bxc3 c5 7.Bc4 Bg7 8.Ne2 O-O 9.Be3 Nc6 10.O-O Bg4 11.f3 Na5 12.Bxf7+ - Great, I can spew a bunch of moves in a line. Now what? I don't know. What if Black doesn't play ...c5 at any point and goes ...Nc6? I don't know.

The positions that result from the Grunfeld make no sense to me what-so-ever. This is why I do not ever play 2.c4 against 1...Nf6 any more. I can play 1.Nf3 and transpose to a Kings Indian or QGD, but avoid the Grunfeld and Nimzo. I have an anti-grunfeld line after 1.Nf3 or 1.c4. I sometime respond to 1...d5 with 2.c4. But I avoid the Grunfeld like the plague from both sides because I know that I do not understand it.

It may be that you don't understand the London. The openings that I truly understand are limited. Queen's Gambit lines (orthodox, Slav, accepted), Kings Indian, Dutch, French, Petroff, etc and specifically avoid those I don't understand and acknowledge that I don't understand them. They would be mostly the Alekhine and Grunfeld - openings with the Mobile pawn center for White.

@thrillerfan Alekhine and Grunfeld openings are fun. Grunfeld himself thought 1 e4 was weak and the Alekhine should be used. 1 e4 Nf6 is highly effective. Grunfeld had a desire to create a new queen pawn defense and his line is incredibly dynamic. Your understanding that they have mobile pawn centers is the beginning of being able to play them. I would love to see you play them.

The Grunfeld is about timing. It is essential to figure when to counterattack. Admittedely, it is delicate. 1 d4 Nf6 2 c4 g6 3 f3 is also a good Anti-Grunfeld.

My point exactly!

Everyone is different. Clearly you sound like a fan of the mobile center. Most people I know that like those positions hate the blocked center (French, Kings Indian, Czech Benoni).

This is why I say if the OP is having trouble with the London, it may be that his thought process and the London don't mix. It will mix for some and not for others.

This is also why when I see posts about "What is your favorite opening?", I just shake my head. Just because I like the Petroff, Dutch, and French doesn't mean everybody will. So asking me that is ridiculous. So you try to learn the French because someone else plays it?

Yours and my situation just proves that. You clearly love the Alekhine and Grunfeld. I hate them more than a root canal. And I am sure there are plenty out there that hate the Trompowsky, English, Sokolsky, Petroff, Dutch, or French, basically my primary repertoire if you combine White (the first 3) and Black (the last 3).

The Sokolsky was my primary opening in 2008-2009, 2014, and mid-2022 to mid-2024. Now I mainly use it for over the board blitz events.

I like the Vienna as White and the Budapest as Black.

@ThrillerFan thank you so much! I will try my best to understand the London, so far I get that it's purpose is to control the center of the board, but that's about it.