Why do you think so?
For example, the largest today empire, United States of America has ALL of it's land conquered.
Maybe the land of North America was free before the European colonization? No, there were natives - Indians, who lived in their own country for thousands years.
Cite from attached Wikipedia article 1: 'Of course, because Amerindians have lived in Americas for 10-20 thousand years, in contrast to the recent post-Colombian colonization wave, they have undoubtedly more right to be called "native" than any other group.'
And what was happened with them?
Very interest document is attached second. It is an extract from Andrew Jackson's Seventh Annual Message to Congress. The title is "Indian removal".
Here is a beginning of that message:
"The plan of removing the aboriginal people who yet remain within the settled portions of the United States to the country west of the Mississippi River approaches its consummation. It was adopted on the most mature consideration of the condition of this race, and ought to be persisted in till the object is accomplished, and prosecuted with as much vigor as a just regard to their circumstances will permit, and as fast as their consent can be obtained. All preceding experiments for the improvement of the Indians have failed. It seems now to be an established fact they they can not live in contact with a civilized community and prosper."
So, they was "removed", as written. Like a useless thing. Two hundred years before this they were watching how their land was shrinking mile by mile and finally Indians was named by Jackson as "the scattered remnants of this race which are left within our borders".
OK, I understand: some nations are expansionist. They can disregard somebody's right of ownership and just come and take all they need.
But what I cannot understand: how they can blame any other nation for doing the same thing?