In History have a peoples been displaced from there land never to have it given back or returned?

It's happened countless times throughout history. It's considered valid, as illustrated by the existence of the secular state of Israel on land taken from the previous residents. Native Americans will never get back the land their ancestors believed belonged to them. Mexicans will never get back the SW US unless they defeat the US in war. The Irish will never get back Northern Ireland unless they can defeat the British in war.

The Saxons will never get back Briton from the Normans. The Incans will never get South America back. The ancient Egyptians will never get Egypt back.

The Toltecs will never get their land back from the Aztecs. The Faraon Apache will never get their land back from the Comanche.

The British will never get India back. The Pakistanis will never get Bengaladesh back. The French will never get Vietnam back. The Japanese will never get Singapore back. The Maori will never get New Zealand back. The aboriginals of Australia will never get Australia back

All the time. In fact, this has happened pretty much everywhere.

The Celts were chased out of Hungary, and ended up in the British Isles, displacing the people already there. Then the Romans came, and ditto. Then the Angles, Saxons, and Jutes the same. And then the Normans, who were Vikings in France, invaded England. In some cases, the invaders and the original inhabitants combined to make a new people, but in other cases, the invaders forced the original inhabitants out (or, they left on their own).

For the first part of your question... in 1755 AD, the English expropriated all the land from the French settlers in "Acadia" (in french it's Acadie) which forced many of them to migrate to the then French colony of Louisiana. Acadia became Nova Scotia which is a province of Canada today. Nova Scotia is latin for New Scotland. The descendants of the "Acadiens" (Acadians) who moved to Louisiana are known today as "Cajuns" from the way the English (Americans) would pronounce the French "Acadiens".

For the second part of your question.... war to acquire land is "not" valid today... this is known as a "war of aggression" & it's against international law. The war crimes trial of Nuremberg Germany of 1946 where Hitler's henchmen were put on trial were found "guilty" of committing a "war of aggression" (amongst other crimes).

Many times. Native American tribes (i.e. "Indians") are a prime example.