Goodness, 11 comments already and no mention of the Balfour Declaration (1917), the correspondences between Sir Henry McMahon and the Sharif of Mecca, Hussein bin Ali (1915-1916), or the Sykes-Picot Agreement of 1916?

During WWI, with the Ottoman Empire allied with Germany and Austria, the British made a lot of promises regarding the disposition and division of the Ottoman controlled lands of Arabia, Syria, and Palestine upon a successful conclusion of the war. The Balfour Declaration, a letter from the British Foreign Secretary, Arthur James Balfour, to Baron Rothschild who served as a representative of Zionists in Britain. The noteworthy quote from this document is this:

His Majesty's government view with favour the establishment in Palestine of a national home for the Jewish people, and will use their best endeavours to facilitate the achievement of this object, it being clearly understood that nothing shall be done which may prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country.

The document speaks for itself, but at the same time, the British, in the hopes of encouraging Arab revolt against the Ottomans, also promised to the Arabs that Great Britain was "prepared to recognize and support the independence of the Arabs within the territories in the limits and boundaries proposed by the Sherif of Mecca", to the exclusion of "[t]he districts of Mersina and Alexandretta, and portions of Syria lying to the west of the districts of Damascus, Homs, Hama and Aleppo." Notably, Palestine is not directly west of Damascus, Homs, Hama, or Aleppo but rather to the South and West. Which means that this statement could easily be interpreted as promising support and recognition for Arab independence in lands that include Palestine.

While one cannot say whether Zionist immigration into Palestine would have still been significant or not had the Balfour Declaration never been made (and later incorporated into the Treaty of Sèvres with the Ottoman Empire and even later the Mandate for Palestine), what can be said is that these two seemingly contradictory promises made by Britain to the Zionists and Arabs were quite central to the competing claims of each party in the formative years of the Arab-Israeli conflict.

Not to gloss over things too much, but the British Mandate for Palestine was the basis for British occupation of Palestine from 1922-1948. During the British occupation, the British struggled to mollify sharply incompatible competing interests as they were overwhelmed by the rising tides of Jewish and Arab nationalism.

The Zionist movement had put real momentum behind Jewish migration to Palestine and the Arabs, none too fond of either British occupation or having to watch as Jews immigrated en mass with the expressed purpose of turning Palestine into a Jewish state, grew restless. The British responded to Arab revolts with the Peel Commission, which for the first time proposed a partitioning of Palestine into Arab and Jewish lands. The Arabs rejected the proposals and revolts resumed. During the Arab revolts, the British used the assistance of Jewish militias to help suppress the revolts.

The British looked to calm Arab opposition in Palestine with the White Paper of 1939 which inter alia restricted Jewish immigration to Palestine and restricted the right of Jews to buy land from Arabs. Of course, in the context of the rise of Nazism in Germany and violent antisemitism elsewhere in Europe, this move was pretty unpopular with the Jews and other supporters of Zionism and turning away desperate Jewish refugees certainly didn't make for good humanitarian publicity. Jewish militias turned against the British occupation and resorted to terrorism against the British as well as the Arabs.

The British stuck it out for the course of WWII, but were clearly ready to wash their hands of it all shortly after. The rest is ... well.. also history.

Oh gosh, where to begin.

In 1915, let's start with the McMahon Correspondences. For those who don't know, these essentially promised the Arabs things, the Arabs being represented (not because he was elected or something, but because he was to be the leader of this shindig) by the Sharif of Mecca, Hussein bin Ali. Hussein was promised, in return for promising to lead an Arab revolt against the Ottomans, that the British would allow for the creation of Arab states across the Middle East, including Palestine. Here's where it gets tricky, though. The British argued that they hadn't meant to include Palestine in this, and perhaps that's true for the central British authorities (hard to know), but McMahon likely did. So they used some wordplay to get out of it later, arguing that they meant a different thing by "district". This would be the first claim of a broken promise by the British, but not the last.

Only two years later (skipping over Sykes Picot as it slighted the French, not the Jews and Arabs), the British decided they wanted to shore up support among Russian Jews for their side (this was WWI, and Russia was faltering), and to thank certain Zionists (ie. Chaim Weizmann) for their contributions to the war effort (he created a new method of acetone production I believe, which helped ammunition production, but I am no chemist). So they put out a vague thing called the Balfour Declaration. It promised a "Jewish National Homeland" in Palestine. This was seen as a direct contradiction the McMahon Correspondences by the Arabs, who were very upset to put it lightly.

But the British weren't done there. After the war ended and they assumed the League of Nations-sanctioned Mandate for Palestine, they decided to split Transjordan from Palestine. This was seen as taking away 75% of the land from a possible Jewish state unfairly, so now Zionists were angry. In 1922, the British issued the Churchill White Paper, which sought to backtrack on Balfour too. It claimed that well, there was no promise of a Jewish state, just a national homeland, and that it would be "in Palestine", but not in all of Palestine. But at the same time, the British were doing many things that made the Arabs unhappy, like allowing Jewish immigration (mainly Zionists), and not giving them proportional representation in the civil administration, or an effective leadership body to rival the Jewish Zionist Organizations like the Histadrut.

But it doesn't stop there of course. I'll skip forward a tad, won't go too far into the 1920, 1921, and 1929 riots, I will just note that the British were seen as playing favorites based on who they blamed each time, and were seen as not doing enough to stop the causes of the riots or the riots themselves. In 1936-1939, there was an Arab revolt in Palestine against the British. The British sought help quelling the revolt without having too many troops or costs, so they allowed Jews to carry weapons. For an Arab to have a weapon was punishable, but not a Jew, and having the Jews help put down the revolt didn't help sectarian strife any. They also recommended a rather nutty partition proposal in 1937, the Peel Commission, which wanted to give the Jews a small portion of the land in the north (the Galilee), while the Arabs would get the rest. But the catch? 250,000 Arabs would have to be "voluntarily" moved out of the future Jewish state. Neither side accepted, understandably.

Then comes 1939. Fearing a continued revolt, and war elsewhere, the British seek to appease the Arabs, so they issue the White Paper of 1939. This restricts Jewish land buying, immigration (go figure, the Holocaust was a time where over 1939-1944 only 75,000 Jews total would be allowed in Palestine; they didn't fill that quota, many going illegally) and saying future immigration would be subject to Arab approval, and promising to attempt to make an Arab state in 10 years. The wary Arabs pretty much rejected it (their leadership wasn't very cohesive, so it's a weird thing to say), saying they wanted an unconditional promise of a state then and there. They would later call for accepting it, but only too late, and it was never really enforced (besides the immigration thing, but a lot of immigration was still done illegally).

Then the British, getting tired and mired in a mess they helped create, decided to abdicate the mandate, shove it at the UN, and stop really enforcing security. It devolved into open Arab-Jewish civil war in the region not long after that, and the British left.

In 1956, the British colluded with Israel and France to attack Egypt in an attempt to topple the Egyptian leader, Gamal Abdel Nasser, but I'd argue by now, the British had already helped the conflict reach a perpetuating state on its own. This is why some Palestinians today curse the British, not the Israelis and not the Americans. They see the British as responsible for the mess.

What I haven't explained here is what the British were after, and I haven't speculated as to whether the conflict would have arisen even if the British took different routes. It absolutely may have, and there's no reason to place the blame for everything on the British either. The Jews and Arabs were dealt bad hands, so to speak, but they also threw a hissy fit of their own, so it's not like all (or even most) of the conflict's blame lays with the British. Just be aware of that.

Britains contribution to Arab-Israeli conflict goes far beyond colonization.

I would even argue that the Suez Crisis had one of the biggest impact on the Arab Israeli conflict.

Suez Crisis was when Egypt decided to nationalize Suez Canal. In essence it was taking it over from Britain and France both of whom had vested interest in the Canal. At this point in time, United States was the leader of the free world as they say, and had a chilly relationship with Israel. Israel at this time was more aligned with the Soviets and had been wanting to get back at its Arab neighbors for the Arab-Israeli war of 1948. Egypt had been recently taken over by the Army who ousted their King, Farouk, and was being lead by Nasser, who was quite popular among the populace and was playing both the Soviets and the Americans for support.

With Nasser nationalizing Suez Canal, Britain and France became quite irate and joined with Israel for a military incursion in to Egypt. This had a dire affect and ramifications on the entire Middle East. Britain and France were seen once more as a foreign threat, an imperialist power trying to colonize Middle East once more, and Israel was seen as an aggressive power, willing to use its military for aggressive purposes. Since Britain and France were part of the alliance which was lead by United States, this invasion by allied forces would alienate Middle East from United States, with possibly falling in to Soviet hands. Eisenhower acted quickly and diplomatically forced France and Britain to give back Suez Canal to Egypt, completely humiliating both nations. Israel was defiant of United States, but eventually backed down.

The Suez Crisis gave massive popularity to Nasser, who would otherwise have been a mediocre leader, from all over the Muslim world. He was seen as the leader of the Muslim world, so much so that Syria decided to become part of Egypt to form United Arab Republic. All this political and diplomatic popularity because United States forced France and Britain to leave Egypt in humiliation. Nasser would go on to bring in the Soviets to the region,(although alienation from United States played a role in this as well) bringing even more agitation and political strife and even more hatred and distrust of the Jews and Israel. I would even argue that Suez Crisis laid down the roots for Six day war and October war, because of the political agitation it created in the Middle East, specifically Israel.