could any of the kingdoms at middle earth attack the southern continents?

[Belegorn]

Originally Posted by Nerwen

But Belegorn and Alfirin, the question being posed is (as far as I can work out, anyway), "why didn't Gondor just go ahead and take over the entire known world?". And possibly more than that, since tom talks about "the southern continent".

I think it was probably a question of manpower as I mentioned in my last post. I believe Ar-Pharazôn took offense to Sauron claiming to be King of the World or some such. Númenor lost a lot of men in its downfall, even the King and his wife. The Dúnedain were few after Númenor's destruction even though there were settlements in M-E before its destruction.

"On the western shores in the days of their power the Númenóreans had maintained many forts and havens for the help of their ships in their great voyages; and the chief of these had been at Pelargir at the mouths of the Anduin in the land that was after called Gondor... Now the people of Elendil were not many, for only a few great ships had escaped the Downfall. There were, it is true, many dwellers upon the west-shores who came in part of the blood of Westernesse, being descended from mariners and wardens of forts set there in the Dark Years; yet all told the Dúnedain were only a small people in the midst of lesser Men." [RotK; ll. The Appendix on Languages]

Númenor's armies were indeed powerful, they being a powerful people in themselves probably playing no small part. Ar-Pharazôn's "armada that took haven at Umbar was so great, and the Númenóreans at their height so terrible and resplendent, that Sauron's servants deserted him." [Letter# 156] I think it is very possible they could have expanded into other realms had they remained intact as a people.

I do not think great casualties are often necessary in these battles. Turenne often won without really fighting based on his marches and positioning. Perhaps, as happened with Sauron's forces, their enemies would lay down their arms.

Originally Posted by tom the eldest

so the only way the gondorians are able to invade the land is by sea

If they had to invade by sea this would not be a problem as they were a maritime power and great sailors and builders of boats.