A chess term. It comes from the German word meaning "compulsion to move". It describes a situation where the unfortunate player is forced to make a move but every possible move only makes his position worse.

The irony is that the best possible move when you are in zugzwang is not to make a move, but the rules declare that the player has to make a move. Forcing your opponent into zugzwang is an elegant way to force a resignation.

An example of zugzwang:

   A                                  H
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    |  8
+----+----+----+----+----+----+----+----+ 
|    |    |    |    |    |    |    |    |
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    | 
+----+----+----+----+----+----+----+----+
|    |    | wK | bp |    |    |    |    | 
+----+----+----+----+----+----+----+----+
|    |    |    | wP | bk |    |    |    | 
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    | 
+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |    | 
+----+----+----+----+----+----+----+----+ 
|    |    |    |    |    |    |    |    |  1
+----+----+----+----+----+----+----+----+
wK - white King
wP - white pawn
bk - black King
bp - black pawn

Whoever has to move will lose because they will have to move their king, leaving their pawn open to capture and eventually to promotion of their opponent's remaining pawn.


Also a great word to play in Scrabble, as you might get to play all seven tiles and get the 50 point bonus. The downside is it needs a blank tile for the extra "Z".

Zugzwang (which in German translates roughly to "the compulsion to move", is one of the most basic principles of simple chess endgames, in which in order to win one side must force the other to move away from a key square in order to promote a pawn. Its application can be studied here. It is most common to find zugzwang positions (in which, if a player were not required to make a move, nothing would be wrong) in positions with extremely reduced material, such as king and pawn endgames.

However, once in a long while a game is played in which a zugzwang position is reached with a large number of pieces remaining. This is very rare because the number of possible moves in a chess game rises sharply with each additional piece on the board.

The most famous example of this kind of position is known as The Immortal Zugzwang Game, and was played by Aron Nimzowitsch against Friedrich Sämisch in Copenhagen, 1923. Both players were extremely strong grandmasters at the time, but Nimzowitsch was on top of the world, having recently systematized chess theory to an unheard-of degree in his groundbreaking book, My System. His style was based on prophylaxis, and he always recommended nullifying the opponent's plans before embarking on one's own. In the following game, he reduces Sämisch to immobility in only 25 moves:


Friedrich Sämisch - Aron Nimzowitsch, Copenhagen, 1923

1.d4 Nf6
2.c4 e6
3.Nf3 b6 (The Queen's Indian Defense)
4.g3 Bb7
5.Bg2 Be7
6.Nc3 O-O
7.O-O d5
8.Ne5 c6
9.cxd5 (Here 9.e4 or 9.b3 are better, with slight advantage for White)
9... cxd5
10.Bf4 a6
11.Rc1 b5
12.Qb3 Nc6
13.Nxc6 Bxc6
14.h3 Qd7
15.Kh2 Nh5 (Over the last few moves White has been playing with no plan, whereas Black has been steadily improving his position. It's now time to start gaining space on the kingside and pushing White's pieces further back.)
16.Bd2 f5
17.Qd1 b4
18.Nb1 Bb5 (Note how Black is moving forward all the time, while White is forced back deep into his own half of the board)
19.Rg1 Bd6
20.e4 (White hopes to free himself with this move, pushing his pawn into the centre of the board and at the same time unveiling an attack on Black's knight on h5, which is now en prise. However, Nimzowitsch chooses to ignore this attack, sacrificing the knight to gain even more space and control over White's position.)
20... fxe4!
21.Qxh5 Rxf2
22.Qg5 Raf8
23.Kh1 R8f5
24.Qe3 Bd3 (In his notes on this game, Nimzowitsch said: "Two pawns, the 7th rank and an enemy Queen's wing which cannot be disentangled, all this for only one piece!")
25.Rce1 h6!! White resigns. The final position is worth close study:

+----+----+----+----+----+----+----+----+
|    |    |    |    |    |    | k  |    |
+----+----+----+----+----+----+----+----+ 
|    |    |    | q  |    |    | p  |    |
+----+----+----+----+----+----+----+----+
| p  |    |    | b  | p  |    |    | p  | 
+----+----+----+----+----+----+----+----+
|    |    |    | p  |    | r  |    |    | 
+----+----+----+----+----+----+----+----+
|    | p  |    | P  | p  |    |    |    | 
+----+----+----+----+----+----+----+----+
|    |    |    | b  | Q  |    | P  | P  | 
+----+----+----+----+----+----+----+----+
| P  | P  |    | B  |    | r  | B  |    | 
+----+----+----+----+----+----+----+----+ 
|    | N  |    |    | R  |    | R  | K  |
+----+----+----+----+----+----+----+----+

    Let's look at White's options, piece by piece.
  • His knight can only move to a3 or c3, both squares attacked by Black's pawn on b4.
  • His bishop has 3 available squares. If it moves to c3 or captures the pawn on b4, it will be captured immediately. If it retreats to c1, the knight on b1 is no longer protected by the rook on e1, and can be captured by Black's d3-bishop.
  • His rook on g1 can only move to f1, where it can be captured by Black's d3-bishop.
  • If his rook on e1 moves at all, then Black plays 26...Re2, winning the White queen, which has no moves. This was the point of 25...h6!!, which removed the queen's escape square on g5.
  • The queen has no moves that do not allow it to be captured.
  • If the bishop on g2 moves to f3 or e4, it is captured immediately. If it moves to f1, then Black plays 26...Rf3 (either rook), winning the White queen, which again has no moves.
  • If the White king moves to h2, its only available square, then 26...R(f5)-f3 wins the queen - the rook cannot be captured by the bishop, which, as a result of White's last move, is now pinned to his king.
  • If White plays 26.g4 to try and shift Black's rook, then 26...R(f5)-f3 wins the queen, since 27.Bxf3 loses immediately to 27...Rh2 checkmate.
  • All White can do is waste a few pawn moves by 26.a3 a5 27.axb4 axb4 28.b3 Kh8 29.h4 Kg8, after which he finds himself in exactly the same dilemma. Zugzwang.

If Sämisch could only avoid making a move, his position would be tenable. However, being forced to move, and not wanting to increase his humiliation by playing the few pointless pawn moves remaining to him, he resigned, and entered the history books as the loser of the Immortal Zugzwang Game.


References:
http://home19.inet.tele.dk/kastanie/check/copen23.htm#immortal
http://www.chess-poster.com/great_games/gg_nimzovich.htm

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