Complex sentence: Japan reluctantly agreed to this, as it was exhausted after the war and in no position to resist without British aid, but this was not forthcoming-instead Britain advised Japan to take the'advice' of the three powers.
Split into simpler sentences: Japan reluctantly agreed to this, as it was exhausted after the war and in no position to resist without British aid, but this was not forthcoming. The British government instead advised Japan to take the'advice' of the three powers.