Some argue that the Bible is contradictory concerning how many fighting men were in Israel and Judah. The argument is that 2 Samuel 24:9 says that there were 800,000 fighting men in Israel and 500,000 fighting men in Judah, while 1 Chronicles 21:5 says that there were 1,100,000 fighting men in Israel and 470,000 fighting men in Judah. However, there are reasonable explanations that solve this alleged contradiction in the Bible.
And Joab gave the sum of the numbering of the people to the king: in Israel there were 800,000 valiant men who drew the sword, and the men of Judah were 500,000.2 Samuel 24:9
And Joab gave the sum of the numbering of the people to David. In all Israel there were 1,100,000 men who drew the sword, and in Judah 470,000 who drew the sword.1 Chronicles 21:5
Regarding the difference in number for Israel, 2 Samuel 24:9 says that there were 800,000 valiant men in Israel, and 1 Chronicles 21:5 says that there were 1,100,000 men.
The most probably explanation is that 2 Samuel 24:9 only counts men who have had battle experience, while 1 Chronicles 21:5 includes 300,000 men who did not have battle experience.
The next verse in 1 Chronicles says this:
But he did not include Levi and Benjamin in the numbering, for the king’s command was abhorrent to Joab.1 Chronicles 21:6
So, the most probable explanation for the different in numbers between 2 Samuel 24:9 and 1 Chronicles 21:5 is that the number in 2 Samuel 24:9 includes the tribes of Levi and Benjamin, while the number in 1 Chronicles 21:5 does not include the tribes of Levi and Benjamin.
There are some foundational principles that apply to all alleged and apparent contradictions in the Bible. To read more, see Bible Difficulties: Foundational Principles.
To read more answers to alleged and apparent contradictions in the Bible, see “Contradictions” in the Bible Answered.
These books are also excellent resources: