Russian President Vladimir Putin has invaded Ukraine, taking his country back toward the halcyon days of the old Soviet Union when Moscow controlled wide swaths of territory, from the Baltic Sea to the Chinese border, and countries like Romania, Bulgaria, Yugoslavia and East Germany looked to the Soviets for leadership.

Under the guise of a “peacekeeping” excursion into eastern Ukraine, Putin sent Russian troops with bombs, missiles and artillery Thursday to start taking back the territory he thinks the Soviet Union should never have lost. Putin said he sent the troops to protect citizens in the separatist areas from Ukrainian aggression, but no one is buying that.

Standing against the Russian troops are the Ukrainian forces and their people, and they are backed by the nations of the world. The U.S., NATO, the European Union and others are responding with aid and arms for Ukraine, and crippling economic sanctions against Russia.

The United States will block the assets of large Russian banks, impose export controls to keep them from getting the high tech equipment it needs. Russian oligarchs, the super-wealthy friends of Putin, are being hit as well with sanctions.

How well these sanctions work will depend on how well the Western nations can hold together. Economic sanction affect not just Russia, but other economies as well. Russia is a major producer of oil and gas. If their distribution is shut down, it will have an impact on oil prices elsewhere.

Putin was aware that these sanctions would be coming. He invaded anyway. Either he is prepared to weather them, or he doesn’t believe the West can keep them up. It is imperative that the United States and its allies keep the pressure on Russia.