OurTorah – hope you don’t mind that I pull you up on your mentioning the 2 and a half tribes remaining behind the Yarden as being a problem in Achdus.
This was endorsed and approved by none other than Moshe Rabenu and then put to action by Yehoshua subject to them participating in the conquest of EY which they did.
If you are looking for the first split in Klal Yisrael, I’d maybe go back even earlier to the Shevatim and their issue with Yosef.
But, please remember we are talking about unfathomably great, highly spiritual men so maybe it’s best not to make comparisons.