Modern day Palestinians are the Arabs who live (or used to live) in the same land that the Zionist Jews now live in. They are primarily the descendants of Ishmael who was the only child produced by Abraham and his wife's handmaid named Hagar (Genesis 16:1 - 4). Hagar and her son were sent away from Abraham and Sarah on two separate occasions (Genesis 16:5 - 6, 21:9 - 14).
Some of the modern-day Palestinians are also likely descendants of Lot (one of Abraham's relatives whose two daughters gave birth to the peoples of Moab and Ammon, Genesis 19:36 - 38). Some are also possibly descended from Esau, the twin brother of Jacob (Israel) and son of Isaac (Genesis 25:25 - 26).
Blessings from Lineage
Although the Palestinians are in Abraham's lineage, they were not given the same blessings and inheritance as Isaac. Although Isaac was Abraham's second son through him, he was the only son produced between himself and his wife Sarah. God himself declared that Isaac would inherit the birthright (firstborn) blessings which included Canaan (Genesis 15:16 - 21, 17:6 - 9, 21:10 - 13 and so on).
And the Lord appeared to him (Isaac) and said, "Do not go down into Egypt. Live in the land which I shall tell you of. Stay in this land, and I will be with you and bless you, for to you and to your seed, I will give all these lands; and I will establish the oath which I swore to Abraham your father. And I will multiply your seed as the stars of the heavens and will give to your seed all these lands . . ." (Genesis 26:2 - 4, HBFV, see also 15:16 - 21, 17:6 - 9, 21:10 - 13).
Uncontrollable People
In an interesting statement that still resonates today, Ishmael, the father of the Palestinians, was prophesied to be a "wild man" who would be constantly fighting with those around him.
And the angel of the Lord said to her (Hagar), "Behold, you are with child, and shall bear a son. And you shall call his name Ishmael because the Lord has heard your affliction. And he will be a wild man. His hand will be against every man, and every man’s hand against him. And he shall live in the presence of all his brothers." (Genesis 16:11 - 12, HBFV).
Moving Back In
Many of the Palestinians have not lived in the land for generations but moved to it after the Zionist movement's economic development created jobs for them. The 2005 World Almanac states regarding the land that "Jewish immigration, begun in the late nineteenth century, swelled in the 1930s with refugees from the Nazis; heavy Arab immigration from Syria and Lebanon also occurred" (page 789).
The famous 19th century writer Mark Twain, living during the time the Ottoman Empire ruled what we now call Israel, remarked how sparsely populated this area was and that it was a desert.
Jewish settlers bought land in Palestine during the British Mandate period and after the Balfour Declaration (which said that the British government was in favor of creating a homeland for the Jews) came into existence in late 1917. This was long before the Palestinians and their rights became a global issue. It was only after these settlers began to improve the land they bought that many Arabs from other locations moved into Israel as well.
The nation of Israel occupied, in 1967, areas known as the West Bank (including East Jerusalem) and the Gaza Strip after its decisive victory in the Six-Day War. Although the Palestinians argue these areas belong to them, and wish to use them to form a future state of Palestine, Israel maintains control of them to this day.
The Conflict
Here is something interesting to consider regarding the Palestinians and their conflict with others. If the existing Arab regimes in the area took in their fellow Arabs and Muslims after 1948, and let them assimilate and immigrate among them, granting them full citizenship, a good portion of the mess we see today in the Middle East would not exist.
Put another way, if the Arab world really treated the Palestinians as their brothers, they would have let them resettle among them. This type of merciful act has occurred in recent history. It happened when India took in Hindus from Pakistan as well as when the nation of Israel took in Jews from the rest of the Middle East.
In summary, the modern-day Palestinians are the Arabs who used to live or who live today in the modern State of Israel, including the occupied territories such as the West Bank and the Gaza Strip. They are primarily the descendants of Ishmael, Abraham's oldest son. Although some have been in the Holy Land for generations, many have not.