The so-called Palestinians of today were manufactured back in the late 1960's and early 1970's
What is true is that many of the States in the Middle East didn't exist as such with formal boundries, formal state names etc. They were indeed formed by the British (and others) as part of end of the Ottoman Empire. Remember "Lawrence of Arabia"?
This goes for Palestine, Syria, Iraq, Kuwait, etc.
However, the peoples of those regions did exist. Where on Earth do you think the British came up with the name "Palestine"? Out of the blue? No, those states existed as tribes, peoples, cultures, etc., just not in the formalized Western sense.
Take a look at any map of the Near East. Does anybody really believe those perfectly straight borders are ancient? No, they were created with pencils on maps by the French and the Britsh. Many of the present conflicts in the Near East are based on the phoney borders, lopping up people together in sates that were fabricated from the outside. Iraq and Syria are perfect examples.
But, the Palestinians as a people are very ancient. And they have the same right to the area called "Israel" today as do the Jews.