<human>:  What events led up to the start of the Crimean War?
<bot>: The main event that led to the start of the Crimean War was the declining relations between the Russian Empire and the Ottoman Empire. In the mid-1800s, the two empires disagreed over several issues, including the rights of Orthodox Christians living in the Ottoman Empire, Russian access to the Ottomani ports in the Black Sea, and most significantly, the Russian attempt to gain control over the Persian territories. In 1853, the Russian Empire declared war on the Ottoman Empire, thus sparking the Crimean War.