The modern day Palestinians are the decedents of the plethora of peoples who have inhabited what is now the State of Palestine and Israel. They, like most of the rest of the Arab world, identify as Arabs due to cultural, linguistic, and religious connections that resulted from the Arab-ization of the Middle East. The concept of "Palestinian," as a national demonym, is a relatively modern concept, a result of the partition of Palestine into the State of Palestine and the State of Israel. While this national identity is indeed a modern conception, the Palestinians are the modern decedents of the peoples who had continuously inhabited the geographic region of Palestine for centuries.

Edit to ask: What do you mean by a "historical group?" It seems to be a very loaded term, and baiting a debate along the lines of whether or not the Palestinians have a legitimate claim to Palestine. I'd just like to note that this subreddit is very cautious about debates, soapboxing and loaded questions.

I haven't seen anyone bite on this question yet, and I think in part this may be due to a hesitancy to reply to the question. First off what do you mean by "an actual historical group?" What political elements are you including into that question? Do people living in Palestine who wanted an independent Arab state count as an "actual historical group" of Palestinians? Or are they only an "actual historical group" if they demand independence from all of the other surrounding Arab states?

If it's the latter then such a group, almost by definition, could not have formed prior to the dissolution of the Ottoman Empire, which is right around the time we start seeing a distinction between the people in the areas that were beginning to be inhabited by Jewish emigrants and those that were not, as found in the responses to the King Crane Commission in 1919. But what might be termed xenophobia or resistance to Zionism is sufficient for, but not determinate of "real" nationalism.

But there are separate aspects to the question in regards to "Arab" identity as well, such that, in particular, Egypt, and Iraq would probably have been viewed in terms of accent/dialect, culture, trade, etc. as being separate from the Levantine provinces of the Ottoman Empire.

And then there's a separate political aspect which is "compared to what?" Usually this question is leading into Israeli claims that although Zionism was aimed at the creation of a Jewish nation in Palestine, the existence of "Palestinians" as a nation post-dates 1948, and as such their demand for statehood is somehow unjustified. I'm not sure I would argue too strongly about the part about Palestinian nationalism, but I would argue with the idea that the early Zionist movement was definitively pushing for a Jewish state themselves prior to, say, the Peel Commission of 1936 as that is not, to my understanding, a major claim or feature of the Zionist movement until the emergence of revisionist Zionism.

There's a few users I'd love to hear from on this question however, and of course your own response as to what you mean, as of course there's a whole separate issue on the connection between Philistines and Palestinians that I know almost nothing about which might be what you're asking about.

Some Palestinian academics like Rashid Khalidi argue that Palestinian national consciousness developed in tandem with Zionist migration. Source: Palestinian Identity: The Construction of Modern National Consciousness

Beshara Doumani argues that Arabs saw themselves as tied to regional cities in his book Rediscovering Palestine: Merchants and Peasants in Jabal Nablus, 1700-1900. For Doumani, regional identity preceded national identity.

Modern Palestinian consciousness (newspapers being a barometer of this) begins to form about 100 years ago, about 30 years after Herzl publishes Der Judenstaat.

I don't know how to answer your question about them being a historical group. I'm not sure what that even means. Are Israelis a historical group?

I just want to mention that while people from Morroco to Yemen identify as "Arab," these groups have significant differences in language, culture, genetics and religion. I speak both Tunisian and Egyptian Arabic, and these dialects are not mutually comprehensible at all. They not only have different vocab, they also have different sentence structures and gender rules.

While moderns define Arabs very broadly, this historically wasn't necessarily the case. Traditionally the term Arab often only referred to nomadic Bedouins or their direct descents. Egyptians, Palestinians, Syrians and North Africans (ie. the vast majority of people we now consider Arab) were generally not included. T.E. Lawrence (ie. Lawrence of Arabia) wrote this in his book the Seven Pillars of Wisdom, comparing the (Bedouin) Arabs he lived with to Egyptians who had come to help the war effort.

Egyptians, being home-loving persons and comfortable, found strangeness always a misery. In this bad instance they suffered hardship for a philanthropic end, which made it harder. They were fighting the Turks, for whom they had a sentimental regard, on behalf of the Arabs, an alien people speaking a language kindred to their own, but appearing therefore all the more unlike in character, and crude in life. The Arabs seemed hostile to the material blessings of civilization rather than appreciative of them. They met with a ribald hoot well-meaning attempts to furnish their bareness.

This alienation between Egyptians and Saudi Bedouins would have been basically the same between Palestinians and North Africans or Sudanese people and Iraqis. While there has been a concerted political effort over the last century to forge a common Arab identity, the alienation between different Arab groups still exists.

On to directly addressing your question, there is a historical precedent for the Palestinian people, but it's complicated.

Broadly speaking, most of the sedentary Arabs living in what is now Syria, Lebanon and Israel/Palestine are Shami or Levantine Arabs. They all speak very similar languages, make similar types of food etc. Since nation states are so new in the Middle East, this was never a national identity per se, but it is a widely recognized cultural identifier.

Under the Ottomans, the Shami lands were split into a couple provinces (vilayets) one of which, Jerusalem Vilayet, had pretty much the same borders as modern-day Palestine. While these vilayets weren't strictly drawn on ethno-national lines, this shows that there was a history of the area having separate elites and administration.

Whether or not Palestinians are a national identity or just a population of Shami Arabs is a controversial, highly politicized question.

Both the Syrian government (which wants to take over Lebanon, Jordan and Israel/Palestine) and the Israelis (who want the Palestinians to become citizens of Arab countries and leave Israel) have played up the historical/cultural connection between the Palestinians and other Shami Arabs for rather self serving reasons.

Most Palestinians and the political groups that represent them reject this association with other Shami people, saying that while there is cultural closeness, they are not Jordanians or Syrians, but Palestinians and deserve their own state Just like Egyptians, Tunisians and Lebanese people do.