Hmm...
An argument could be made for historical Babylon (real Babylon, not the mythical nation of evil/prophecy Babylon). It was one of the earliest empires of record and King Hammurrabi's stele of law is the blueprint upon which all subsequent nation states central code of law is based upon, as well as being one of the first nations to instill taxation and service contract guidelines. Babylon (and Egypt) are the templates which modern countries, as well as several of their contemporaries, were based upon when it comes to laws, trade, and currency.
A good argument could also be made for China as well with their innovations in literature and the invention of the printing press and what that has done for society, as well as their innovations in philosophy and war.
An argument could also be made for Israel as well. While not dominating world events from a martial or imperialistic standpoint, the Abrahamic religion Judaism which sprung forth from Israel has had a huge influence on the world as a whole and has been integral to many major world events (though that opens the Monotheistic Regress argument and you'd have to bring up Zoroastrianism and Atenism).
Then of course, obviously, there's Rome and Britain which dominated world events on a grand scale through commerce and imperialism. Of the two I'd give the nod to Rome as they also had innovations in representative government which became a blueprint for subsequent nations, while Britain and European Culture as a whole has dominated the last few centuries. Rome borrowed heavily from Greece who in turn borrowed heavily from Egypt/Kemet, and actually absorbed those two former empires and co-opted a lot of their customs.
There's really no definitive answer. It's just a matter of what you're looking for.