One nagging fear in Britain is the…
1852 CE to 1863 CE
It is well understood that a collapse of that country would set off a scramble for its territory and possibly plunge Britain into war.
To head this off, Britain seeks to keep the Russians from occupying Constantinople and taking over the Bosporous Straits, as well as from threatening India via Afghanistan.
In 1853, Britain and France intervene in the Crimean War and defeat Russia at a very high cost in casualties.