In the 1850s, Russia tried to expand into the Ottoman Empire. This led to a war with Britain and France, which had allied with the Ottomans to stop Russian aggression. The war's primary focus was along the border of Russia and the Ottoman Empire in Europe. It was a short but violent conflict, with nearly a million casualties.
Alaska was far from the principal fighting, and Britain and Russia agreed to a truce in the Pacific Northwest. Both nations agreed not to attack North American settlements. Neither side wanted to disturb profits from their businesses there. The British and French did attack Kamchatka in 1854 and 1855, occupying the Russian city of Petropavlovsk. The Tlingit, hoping the war had weakened Russians in Alaska, used the opportunity to mount a large attack on Sitka in 1855. The attack was unsuccessful but showed Tlingit's continued threat in the Southeast.
The war ended in 1856 with Russia's defeat and was costly for her. Russia suffered heavy losses, with over 400,000 men killed. The treasury was empty, and the government was in heavy debt.
The Crimean War also showed Russia that her hold on Alaska was tenuous. Britain's superior naval power would make holding Alaska difficult if war came to the region. If the Russians could not successfully protect Kamchatka in the Russian mainland against an invading force, how would they be able to protect Sitka or Kodiak?
And it was not just Britain that Russia was worried about. Russia and America had friendly relations and extensive trade in the Pacific. However, 300,000 Americans migrated to California within a few years during the gold rush. With only around 500 Russians in Alaska, it was easy to imagine the colony being overwhelmed by Americans in the future.
1855 Siege of Petropavlovsk