A country in Central Asia, one of the 'stans, formerly part of the Soviet Union, and long long before that, part of the one or the other Persian Empire. It is subject to the cliche that it actually is a Turkic country. It is therefore only appropriate for Tajikistan in future histories (and sometimes ATLs, too) to join a powerful Pan-Turkestan whenever it emerges. What? Never mind the fact that the Tajiks actually speak a variety of Persian.
See also Romania for a European country about which similar misconceptions exist.
The misconception may have arisen because Tajikistan is the 'stan with the least defining characteristics: Kazakhstan has Borat and space, Uzbekistan has Rommy, Turkmenistan had that dictator who made Kim Jong Il look sane and has since been replaced with one who sounds like a scouts' chant, and Kyrgyzstan is impossible to spell.
None that we know of.