That's, yeah, a really difficult question to answer, in part because I think the answer changes pretty substantially between those two dates in question "WWI and 1948." You also need to separate out what "nationalism" you're talking about, whether that's a pan-Arab nationalism, a greater Syrian nationalism, a Palestinian nationalism or a Zionist nationalism, and if we're talking about a Zionist nationalism what kind of Zionism (e.g. Labor Zionism? Revisionist Zionism?).

I think you also need to be very careful with the distinction between violence that is "nationalistic" as opposed to merely xenophobic. In the 1936-39 revolt, Arabs might well have attacked Jews on the basis of being "the other" and vice versa but did either side aspire to a nation, and if so in what form?

I am by no means a Palestine/Israel specialist and this is quite possibly the most specialized subject in the entire region so I'm hesitant to "answer" your question but I think I can at least point you to some other works that might be helpful:

• The King-Crane Commission Report - an incredibly important primary source that basically consists of a series of pseudo-polls about Arab aspirations in the region.
• The Revolt by Menachem Begin, a first hand account of the Irgun, also just a great read, particularly interesting for those years prior to the outbreak of civil conflict in 1947 when large parts of the Zionist movement were still at least ostensibly claiming that they were not aiming for the creation of an independent Jewish nation-state.
• One Palestine, Complete by Tom Segev, a bit on the pop-narrative side, but I quite like it as a history of the buildup to '48.
• The Arab Awakening by George Antonius, this should practically be treated as primary source material but it's the source of much the argument that the Arab revolt in WWI was nationalist in its character. If you want to argue an early date for the emergence of Arab nationalism in Palestine I would say this would be a good place to start.
• Any discussion of this is also going to have to deal with the precise language of the Balfour declaration and what it means to have a Jewish national home in Palestine and how that might differ from a nation. This has been written about endlessly, I'm not sure there is a good answer because I'm not convinced that Balfour had any idea what he was doing, but that's another question for another day.

Also I would have a look at some of the literature on the meaning of nationalism discussed in this thread based on my own question about the topic here because, as I said, one of the key distinctions I think you'll have to make is whether conflict with "the other" along "national" lines is actually a form of "nationalist" conflict.

Like I personally don't see the need to talk about religion.

You're free to take this as you like, but if you think religion isn't relevant then you very much should talk about it. A well-constructed essay needs to address and refute counter-arguments as much as it supports your own views. One aspect that might be worth discussing on this particularly question, although you might be limited by length and scope, is why the outbreak of civil conflict in Palestine also saw Arab attacks on non-Zionist Jews in countries like Egypt (where the Muslim Brotherhood carried out a campaign of violence against Egyptian Jews who were basically minding their own business.) Or within Palestine why the 1929 riots seem to have been so focused on religious holy sites etc.

Again, a huge question and I'm sorry if it's not an "answer" per se, but this is one of the biggies in the field and whole books have been written on this debate, which shows no signs of slowing down.