[ilamont]

Mutual defense treaties have a poor track record in the face of heavily armed, aggressive regimes playing up real or imagined injustices while undermining political and military obstacles. If the alliance is weak, disaster can result.

Examples abound - Poland and France both had mutual defense treaties with various allies that failed when Germany invaded. In Japan's backyard, the Philippines lost territory in the South China Sea to China after it decided to cut ties with the U.S. military. As soon as the U.S. pulled away, the Chinese PLA moved right in. An international tribunal in The Hague ruled China's actions were completely illegal, but China has since strengthened its hold by building landing strips and military fortifications on the reefs and small islets.

The Japan/U.S. alliance is strong, but relationships and power profiles can change. Xi's not going anywhere, and he can play the long game when it comes to the Diaoyutai and other territorial claims.

[rbp]

Minor quibble - UK entered WW2 because of their mutual defense treaty with Poland