Not just American division, but NATO/EU division. His base case scenario as far as a Western response was probably a watered-down sanctions package, consisting of incrementally stiffer sanctions on some banks and oligarchs. Honestly, that's what I thought the West would do as well.
One of Putin's other military options (what I thought he was going to end up doing), moving troops/tanks into the newly "independent" areas inside of eastern Ukraine and then using that as a base of operations to destabilize the Ukraine government over the next few years, probably looks attractive right now. He had to do something - he'd lose all kinds of international legitimacy if he massed troops to that level and made those very specific demands, then did nothing when NATO inevitably wouldn't give in to those demands.
That would have brought out the incremental sanctions and he'd have a while to plot his next move. Instead he dropped the frog right into the boiling water and it jumped right out. I think he's feeling time pressure, like Russia's window to do something like this is closing, and he needed the more aggressive action now.