All areas of the world have been conquered numerous times in history (or prehistory). If you mean modern states as they exist now, few have actually been conquered. For example, Germany as it exists now only came into existence at the reunification in 1990. It hasn't been conquered since then, but the territory itself has been invaded/conquered/occupied times and again. The last time was by Allied forces at the end of WWII and WWI. Before that, Prussia (over half of which lied in modern Poland) conquered and unified the various German kingdoms, duchies, principalities and counties. Napoleon conquered Germany in 1806. In the early Middle Age, most of Germany was conquered by the Franks (who were based around modern Belgium), and earlier still by the Huns. Let us not forget too that the south-west of Germany was annexed by Rome and approximately half of modern Germany was defeated and occupied by the Romans (as far as the Danish border). You can go back even further with the Celts and Germans invading the region in the Bronze Age.
The same kind of scenario holds for any place on Earth. Australia, the Pacific Islands and Japan were probably the least invaded/conquered places since humans first set foot there. Australia and the Pacific Islands were only colonised once by Europeans after their indigenous populations got there, and never since. Japan was progressively conquered by the Yayoi people starting 2500 years ago, and since then was only successfully occupied by a foreign power in 1945.
The same kind of scenario holds for any place on Earth. Australia, the Pacific Islands and Japan were probably the least invaded/conquered places since humans first set foot there. Australia and the Pacific Islands were only colonised once by Europeans after their indigenous populations got there, and never since. Japan was progressively conquered by the Yayoi people starting 2500 years ago, and since then was only successfully occupied by a foreign power in 1945.