Both the Kingdom of Israel and the Kingdom of Judah had common Hebrew roots and were "Children of Israel."
Both were doing fine when Assyrians decided to intervene as noted
here. Allah Almighty did
not distinguish these two kingdoms and confirm that the Kingdom of Judah was better than the Kingdom of Israel in the promised land and was spared:
"And We warned the Children of Israel in the Scripture, “You will certainly cause corruption in the land twice, and you will become extremely arrogant." (17:4)
"When the first of the two warnings would come to pass, We would send against you some of Our servants of great might, who would ravage your homes. This would be a warning fulfilled." (17:5)
"Then ˹after your repentance˺ We would give you the upper hand over them and aid you with wealth and offspring, causing you to outnumber them." (17:6)
"If you act rightly, it is for your own good, but if you do wrong, it is to your own loss. “And when the second warning would come to pass, your enemies would ˹be left to˺ totally disgrace you and enter that place of worship as they entered it the first time, and utterly destroy whatever would fall into their hands." (17:7)
Allah Almighty pointed out that these people became corrupt and arrogant and he punished them by creating conditions of war in the region.
Assyrians and Babylonians are same people and destroyed both the kingdom of Israel and the Kingdom of Judah in succession but Hebrews regrouped and recovered from this setback and defeated Babylonians in this prolonged war, and established the Hasmonean dynasty in the promised land but Romans destroyed the Hasmonean dynasty in another war.
Two different wars are hinted in the revelations mentioned above - each was a warning to Hebrews to mend their ways. Hebrews lost to the first enemy but regrouped and defeated it at a later stage. But Hebrews could not handle the second enemy. Baybalonians destroyed the First Temple in war while Romans destroyed the Second Temple in war.
Division between the Kingdom of Judah and the Kingdom of Israel was on political grounds like in Muslim-majority countries in modern times (Pakistan vs. Bangladesh), it does not change the fundamental fact that both were created by the "Children of Israel" in the promised land and this is how Allah Almighty mentioned these people.
And it is not surprising that both Hebrew kingdoms fought each other because Muslim-majority countries also fight each other. And we also see corruption and arrogance in some Muslim-majority countries. Therefore, some regions are not peaceful.
I see repeat of same story in current times. If this trend continues then a truly destructive war is possible in which many will die. Think about it.
Therefore, all need to reflect and think about how to solve current disputes in a better way.