[Snowdog]

I believe Gondor had a civil war over this very subject. When King Valacar married Vidumavi, the daughter of the Rhovanion king Vidugavia, a split in the thoughts of Gondorians began when Valacar's son Eldacar was born.

Seen as a 'half-breed' by many, when Valacar died and Eldacar became king, an open revolt commenced with Castamir, a distant cousin and contemporary of Eldacar's claimed the throne due to having 'pure Numenorean blood'.

They both were great grandsons of King Calmacil and their grandfathers were brothers, and things went badly for Gondor after King Valacar died and 1432. By 1437, Castamir's forces managed to breakthrough north and capture Minas Anor and sack Osgiliath, and this is when the Dome of the Starts in Osgiliath was destroyed and the Palantir it housed was lost in the Anduin River.

Eldacar was driven out and retreated north to Rhovania and Castamir became King of Gondor. But he was a crappy King, and he lost support and built ships and thought only of the sea while eldacar gathered his strength and marched south to reclaim the throne in 1447. Castamir was slain and his sons fled to Umbar on the ships and became the source of pain for Gnodor from that time onward.

Were the Castamirian Gondorians stonger than the mixed Gondorian/Northman army of Eldacar, not likely.

The Dunedain of the North held to keeping their bloodlines 'pure', which considering the small population, leads to its own questions. Maybe they lived longer than the now-long-mingled Gondorians in the late third age