Definition
When armies engage in battle, they commence fighting.
（军队）开始战斗；交战
The two armies joined battle at the border region.
两支军队在边境地区交战。
As the horns sounded, the soldiers joined battle.
号角声响起时，士兵们开始战斗。
In the desert, they joined battle and fought for hours.
在沙漠中，他们交战并打了几个小时。