"Besiege Wei to Rescue Zhao" comes from a very famous battle in the Warring States Period. The battle fully displayed the military talent of a great strategist of the time, Sun Bin.

The battle was actually between Sun Bin and Pang Juan, a general of the state of Wei. The two had once followed same teacher to learn military strategies and had both served in Wei. But Pan Juan persecuted Sun Bin out of jealousy of his military talent, and the two went on different paths. Sun Bin fled Wei to be a military councilor for the state of Qi.

Pang Juan was leading his army in an attack upon a smaller state Zhao. The capital besieged, the king of Zhao sent a man to another stronger state of Qi, asking for assistance. In response to Zhao's entreaty, the king of Qi appointed general Tian Ji  and the strategist Sun Bin as military counselor to help out Zhao.

Before they started off, they discussed the situation and their plan. Tian Ji intended to fight Pan Juan face to face, but Sun Bing didn't agree, saying that might result in Qi army's unnecessary loss.

However, he reasoned: "Now that the troops of Wei are in Zhao, its capital must be empty. This presents a best chance for us. If we surround Wei's capital, Pang Juan will be obliged to withdraw from Zhao. On the other hand, the Wei troops, tired out already, after so long a fright, will be made even more exhausted, rushing backward to protected their capital, capital we, comfortable and free from worry, may have a good test when waiting at our ease in an ideal position, and get well prepared for a sudden attack."

Tian Ji took this advice and marched toward the capital of Wei. Everything afterward went as expected. The Wei troops had to retreat, hearing that their capital was in danger. When they got to a valley, the soldiers of Qi, lying in ambush, suddenly dashed out and defeated the Wei Army utterly. Pan Juan was also later killed in battle with Sun Bin.