Complex sentence: On 18 December 1800, Emperor Paul I declared Kartli-Kakheti annexed to the Russian Empire, although full implementation was left in abeyance, and Tsar Paul was assassinated in March 1801.
Split into simpler sentences: On 18 December 1800, Tsar Paul I declared Kartli-Kakheti annexed to the Russian Empire. The actual annexation was left in abeyance and Tsar Paul was assassinated in March 1801.