The correct answer to this open question is the following.
European countries that had territory that was no longer within Russian boundaries because of the Brest-Litovsk Treaty were parts of Polan, Ukraine, Finland, and the Baltic provinces.
On March 3, 1918, the Brest-Litovsk Treaty was signed to bring peace between the new government of Russia (the Soviets) and the so-called Central Powers of Austria-Hungary, Germany, the Ottoman Empire, and Bulgaria. That was the end of the Russians participation in World War 1. The treaty only lasted nine months. It was terminated in November 1918.
