With the unlawful invasion of Ukraine, Russian President Vladimir Putin has blown up the post–Cold War era. The supposed Pax Americana of the past three decades—which featured far too little pax—is over. What comes next is yet to be defined, with a stark contrast between what might be possible and what appears likely to follow. Is a new and more dangerous, militarized Cold War inevitable? Is another world of mutual security still conceivable?

The first moral imperative is to bring the war in Ukraine to an end. Given Putin’s miscalculations, the stirring resistance of the Ukrainians, and the aid and arms provided by a united NATO, a brutal and costly battle, block by block, through Ukraine’s cities and towns is now probable.

That would exact a horrendous price, paid by Ukrainians with their lives and the destruction of their country. Instead, the main objective must be to stop the fighting as quickly as possible—sparing Ukrainian cities from further bombing and allowing for the safe evacuation of refugees. This will require a global demand for a cease-fire, followed by a negotiated settlement that inevitably requires difficult compromises.

Read the full text of Katrina’s column here.