New Living Translation
In the spring of the year, when kings normally go out to war, Joab led the Israelite army in successful attacks against the land of the Ammonites. In the process he laid siege to the city of Rabbah, attacking and destroying it. However, David stayed behind in Jerusalem.

American Standard Version
And it came to pass, at the time of the return of the year, at the time when kings go out to battle , that Joab led forth the army, and wasted the country of the children of Ammon, and came and besieged Rabbah. But David tarried at Jerusalem. And Joab smote Rabbah, and overthrew it.

Berean Study Bible
In the spring, at the time when kings march out to war, Joab led out the army and ravaged the land of the Ammonites. He came to Rabbah and besieged it, but David remained in Jerusalem. And Joab attacked Rabbah and demolished it.

Douay-Rheims Bible
And it came to pass after the course of a year, at the time that kings go out to battle, Joab gathered together an army and the strength of the troops, and wasted the land of the children of Ammon: and went and besieged Rabba. But David stayed at Jerusalem, when Joab smote Rabba, and destroyed it.

English Revised Version
And it came to pass, at the time of the return of the year, at the time when kings go out to battle, that Joab led forth the power of the army, and wasted the country of the children of Ammon, and came and besieged Rabbah. But David tarried at Jerusalem. And Joab smote Rabbah, and overthrew it.

King James Bible
And it came to pass, that after the year was expired, at the time that kings go out to battle, Joab led forth the power of the army, and wasted the country of the children of Ammon, and came and besieged Rabbah. But David tarried at Jerusalem. And Joab smote Rabbah, and destroyed it.

World English Bible
It happened, at the time of the return of the year, at the time when kings go out [to battle], that Joab led forth the army, and wasted the country of the children of Ammon, and came and besieged Rabbah. But David stayed at Jerusalem. Joab struck Rabbah, and overthrew it.

Young's Literal Translation
And it cometh to pass, at the time of the turn of the year -- at the time of the going out of the messengers -- that Joab leadeth out the force of the host, and destroyeth the land of the sons of Ammon, and cometh in and beseigeth Rabbah -- David is abiding in Jerusalem -- and Joab smiteth Rabbah, and breaketh it down.

1 Chronicles 20:1 Additional Translations ...