 Complete the following phrase:  Romania had entered World War I in August 1916, invading Austria-Hungary in an attempt to seize Transylvania. However, the Central Powers launched a successful counteroffensive in September 1916, capturing Bucharest and occupying approximately two thirds of the Romanian territory by December 1916. The Romanian government was forced to retreat to Iași, in the historical region of Moldavia, but was able to stave off complete collapse thanks to the numerous Russian reinforcements that had been sent to Romania to prevent a Central Power invasion of southern Russia at the beginning of 1917, and later, in spite of the unwillingness of the Russian troops to continue fighting, thanks to the successful repulse of the Central Powers offensive at Mărășești and 