The football tournament was meant to be held in the United Arab Emirates, which is close to Saudi Arabia and Iran.
But Fifa are worried the players might be in danger if the US starts to bomb Iraq in a possible war.
The war could affect nearby countries like Iran.
The championship was supposed to start on 25 March, but the disappointed young players will have to wait until Fifa think it's safer.
The England Under-20s coach Les Reed said it was a sensible decision to make and was not a surprise.
But he hopes Fifa decide to choose another country to host the tournament in the summer.
This would be good news for England because the league season would have ended by then. This means the squad would be a lot stronger.
Twenty-four nations were meant to take part, including England, the USA and Spain.
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