The Muslims were there first and basically all they're asking for (besides the minority of extremists; the rest of the terrorists - who are also a minority I might add - join up with them because they grow up in apartheid ghettos under military occupation with no human rights) is to be able to live in their own country in peace
I just want to say, this is more complicated than you're making it out to be. The Jews were there firster. Both groups have incorporated the land into the traditions at the roots of their cultures. It's not so easy as to say that one side has a legitimate claim and the other doesn't.
Far be it from me to say that "Jews" as an abstract, conglomerated entity have less of a claim than "Palestinians," as same, to that piece of land. Such a statement is meaningless, which is why a number of they key rationalizations for Zionism are dumb (the religious one that God said so, and the secular one that Jews once had a kingdom there, therefore any random American or European who happens to be Jewish has more of a right to live there than do the locals. The one that wasn't dumb is the argument that nowhere in the world is safe for Jews, which in the early 20th century was indisputably true. Its not true any longer, but that's another story).
In any case, the argument that "The Jews were there firster" is also dumb for a number of reasons. Let me break it down, starting with its assumptions.
Assumption 1: The actions or ways of living of people 3000 years ago should directly affect our assessment of human rights today.
To this assumption, I can only say, wtf are you smoking? Obviously nobody would state this as a principle outright, but it underlies the argument that "Jews have a right to live in Palestine because their distant ancestors did." Anyway, does that mean that since I'm a German, and 2000 years ago my ancestors were rampaging around Central Asia, I have the right to show up in Central Asia and establish a state that favors my ethnicity while disenfranchising the locals? Or that as a Mennonite, I have the right to show up in Switzerland and do the same? The idea that the way things were 3000 years ago should be held as a claim to anything is completely absurd on its face.
Secondly, the Palestinians were there first, as in, today's Palestinians are from the population that had continuously been living in Palestine not only for the past few centuries, but in many cases since the times of the Jews (and many of them WERE Jews, but I'll get to that later) AND before. Remember those Canaanites in the Bible? You better believe many Palestinians AND Jews could trace their ancestries back to those people. And THOSE people weren't the first either.
But today's Palestinians were the ones there in living memory. There are people still alive who were exiled in 1948, had their homes and land (i.e., livelihood, since they were mostly farmers) seized, and were never allowed to return to what became Israel, while any random-ass American who happened to have a Jewish grandparent WAS allowed to come there and live happily on their land while they languished in refugee camps. Same thing happened again in 67 in smaller numbers. No reasonable person can dispute that someone who lived in Palestine in 1948 had a right to. You can make quite strong arguments that their children and grandchildren (today's terrorists, btw, since they've grown up under martial law and/or in hellhole ghettos, ghettos in the European sense) have a right to. But how the hell do you make an argument that Joe McAmerican whose grandmother was Jewish has some innate right to live there, especially while people who were kicked off that land are not being allowed to return?
Assumption 2: "Jews" are a distinct and separate lineage from the rest of humanity, and as such can be traced directly back to the Kingdom of Judah of 2500 years ago.
Again, nobody would straight up admit they believed this, but the assumption underlies arguments behind why something like the "Law of 'Return'" should exist. But the thing is, people intermix. Ethnic identities are basically culturally constructed, much as I hate that term. People's ancestries are intertangled. Every generation a person traces their lineage back, the number of direct ancestors DOUBLES, until you start to hit overlap due to inbreeding or due to the number becoming larger than the population of Earth. Any European or European-American probably has a significant number of Jewish ancestors, and any European Jewish person has a significant number of Gentile ancestors (why do you think Jewish people look like the people around them instead of like Levantine farmers?). Palestinian Arabs certainly have lot of Jewish ancestors. Palestinian Christians have the longest Christian tradition of all, obviously since Jesus lived there, and the first Christians were of course Jews. You better believe some of their massive number of ancestors were early Jewish converts to Christianity. Similar with Muslims, of the Jews left in Palestine when the Muslims invaded, a number certainly converted, voluntary or forced. Basic population genetics makes it really absurd except in terms of studying culture to say that ethnic groups are somehow distinct in terms of descent, if they've shared the same geographic area at all at any point in their history.
Anyway, this post is already well into the pits of tl;dr oblivion so I'm just going to close by saying that it's totally fucktarded to say a given person has some innate right to live in a certain place more so than does the rest of humanity, simply because they belong to a certain ethnic group. The only reasonable standard is, have they and their family been living there and been settled there for a long time? Do they have their livelihood invested in it? Obviously, the answer is "yes" for basically all Palestinians, and for native-born Israelis to a lesser extent since they're mostly the children or even grandchildren of immigrants, and a resounding "no" for anybody whose ancestry was in any other part of the world for the past millennium, no matter what their self-identification. Now I'm of the opinion that anybody should be allowed to live anywhere in the world they want, regardless of ethnicity and of claims of God's promises to mythical ancestors, as long as they're willing to respect the people who are there already and play by their rules and most of all, not fuck them over using superior military power. If the fledgling state of Israel had played by those rules, everyone could be living happily in parallel, if not together. And to sum it up, Jews don't have a right to live in Palestine because their distant ancestors did. They have a right to live there because they're humans, and humans should have the right to live wherever they want as long as they respect the place and its inhabitants who were there when they arrived. period.
Edit: Sergius already made one of my points quite well, albeit in less detail.
Also, to anticipate the argument that "Well fledgling Israel tried to play by those rules but the Arabs attacked them!" - yeah, the Arabs attacked them. The Palestinians didn't. The Palestinians were a bunch of farmers minding their business (and, I should add, living by and large on quite good terms with their Jewish neighbors, included recent immigrants). The Arabs in this case were the armies of neighboring countries run by asshole dictators. I know some Israelis and the pro-Israel crowd love to refer to Palestinians as just "Arabs" since it lumps them in with the rest of the Arab world as if they're indistinguishable, serving many propaganda purposes I won't bother listing. but keep in mind who attacked Israel (it wasn't the Palestinians) and who got fucked in the ass because of it (it was the Palestinians)