I think you are correct in your comparison of the USSR and China. We in the US often see independence as the natural progression for some countries. However, while it would have been difficult or impossible for a republic to break away from the USSR in an earlier time, given the circumstances of 1991 and the existence of the USSR even if they could republics might not want to have broken away. The fear of some of them could have been how would they maintain their independence from neighboring countries other than the USSR. Also, the US would have wanted Kazakstan and the Ukraine to stay within the USSR because of their nuclear missiles. Also, while we generally believe independence is progress that was not the case in the former USSR. Most of the former Soviet Republics became dictatorships that adored Stalin. The USSR was a lesser danger to the US and world peace than the independent Soviet Republics. The structure of the USSR had it's faults but it's fall was not the sure thing that people now see so clearly. The Russian Empire/USSR had stood for hundreds of years and if Iran had been more powerful some republics might not have wanted to break away. If China hadn't had the demonstrations in Tiananmen Square and was in a stronger position in terms of foreign affairs, it could have been different for the USSR regardless of it's faults.