>and you didn't have to plan to wage a war against the whole world at the same time.
A plan to wage war against the whole world is a bad plan.
Per Xima and Sun Tzu teaching: you should be well acquainted with your neighbors and gain their support in war.
Your enemy should be isolated and friend-less, which would make the war end quicker.
By fighting against allied country, you risk prolonging the war and losing.