Why did the game declare a draw?

In addition to stalemate (covered in another question), the game can end in a forced draw. Either of the following conditions can trigger a draw:

• insufficient material – a king, even aided by a bishop or knight, cannot win against a lone king.
• three-fold repetition – if the same position occurs 3 times, the game ends in a draw. This can happen in late game, when the same pieces move back and forth in a pattern.
• 50 pawnless moves without captures- self-explanatory, this avoids long, tedious games.

In multiplayer, the two players can also end the game in draw by agreement.