Complex sentence: The internationally recognised Ukrainian territory of Crimea was annexed by the Russian Federation on 18 March 2014 and from that time has been "de facto" administered as two federal subjects--the Republic of Crimea and the city of Sevastopol--within the Crimean Federal District.
Split into simpler sentences: The internationally recognised Ukrainian territory of Crimea was annexed by the Russian Federation in March 2014. From the time of the annexation on 18 March 2014, Russia has been "de facto" administered as two federal subjects--the Republic of Crimea and the city of Sevastopol--within the Crimean Federal District.