Leagues are commonly made for mutual defense.

结成联盟往往是为了共同防御。

《新英汉大辞典》

He hoped the defense authorities of the two countries could strengthen exchanges and communication to promote mutual trust and avoid misunderstanding and misjudgment.

希望两国防卫部门进一步加强交流与沟通，增进互信，防止误解和误判。

youdao

ACE and the insured reach the mutual agreement on the defense strategy.

ACE与被保险人就抗辩策达成一致。

youdao

Syria perhaps rises to the level of rook, since it is a nation-state and has a mutual defense treaty with Iran.

CENTERFORSECURITYPOLICY: Next Steps in the Iran Crisis

"It's well known that the United States and Japan have a mutual defense treaty, " a defense official said of Panetta's exchange in Beijing.

CENTERFORSECURITYPOLICY: Center For Security Policy

Many of the changes the treaty was due to usher in -- such as a mutual defense clause -- were largely symbolic in nature.

CENTERFORSECURITYPOLICY: Europe after Lisbon