All leagues are hostile with one another in default setting.

If you apply to ally with one league, only with their approval can it come into effect.

If you apply to become neutral with allied leagues, it comes into effect immediately.

If you apply to become neutral with hostile leagues, only with their approval can it come into effect.

If you apply to be hostile with one league, it will come into effect in an hour.

You can tap on league icon and select Diplomacy to view your league diplomacy.