Hey, normally I just ghost the forums, but I saw this topic (which seemed like a fairly good one) going to waste so I thought I'd step in. First post

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Well, one of the main diffrences in the two situations was that Gondor was actually under serious threat from Rhun and Harad whereas Numenor was more or less completely safe from the peoples they conquered. This in itself is essentially justification for Gondor's actions, but beyond that Numenor also conquered out of greed (unlike Gondor).
The Akallabêth says:
Quote:
But those who lived turned more eagerly to pleasure and revelry, desiring ever more goods and more riches...
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and
Quote:
Thus it came to pass in that time that the Númenóreans first made great settlements upon the west shores of the ancient lands; for their own land now seemed to them shrunken, and they had no rest or content therein, and they desired now wealth and dominion in Middle-earth, since the West was denied. Great harbours and strong towers they made, and there many of them took up their abode; but they appeared now rather as lords and masters and gatherers of tribute than as helpers and teachers.
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(Italics added for embellishment).
This is quite to the contrary of what Gondor was doing. Where Numenor solely seeked to exploit the lands and peoples under it's dominion (well, at least the "colonies" under it's dominion) Gondor seeked protection. Gondor's aim was to keep Harad and Rhun under control, and the easiest way to do that was to rule them. It probably didn't make the men of Harad and Rhun very happy, but it was in the best interest of Gondor (and Gondor's allies) to keep Harad and Rhun restrained. It's much easier to prosper when your not under the constant threat of attack.
So, in essence, it boils down to intention.