Well, some are very unlikely candidates. India, if not for the Mughals, Romania, if not for 19th century nationalism, the US in its current form.
I mean, do you think that average 15th century Indian subcontinent dweller would have thought you were not crazy if you had said:
"Some random guy, a distant relative of Timur Lenk, will create a country which will cover all of India."
Same for the Romanian peasant:
"After 2 wars the Great Powers will agree to liberate the Romanian provinces and let them unite into a single country. The ruler of this union will not be killed by an ally 1 year after the union, like
his historical predecessor."
Or the US:
"The French will sell 2 million square kilometers to a small country created by former English colonies. The Russians will sell 1.5 million kilometers more. This small country will conquer about 3 million more from a Spanish colonial country".