A formal inquiry commission, headed by Sir Thomas Haycraft, Chief Justice of Palestine, found:
"The fundamental cause of the Jaffa riots and the subsequent acts of violence was a feeling among the Arabs of discontent with, and hostility to, the Jews, due to political and economic causes, and connected with Jewish immigration, and with their conception of Zionist policy as derived from Jewish exponents.
"The immediate cause of the Jaffa riots on the 1st May was an unauthorized demonstration of Bolshevik Jews, followed by its clash with an authorized demonstration of the Jewish Labour Party.
"The racial strife was begun by Arabs, and rapidly developed into a conflict of great violence between Arabs and Jews, in which the Arab majority, who were generally the aggressors, inflicted most of the casualties.
"The outbreak was not premeditated or expected, nor was either side prepared for it; but the state of popular feeling made a conflict likely to occur on any provocation by any Jews ..."
On its causes:
"... After examining this and other evidence and studying the course of events in Palestine since the War, we have no doubt as to what were 'the underlying causes of the disturbances' of last year. They were:
"(i) The desire of the Arabs for national independence.
"(ii) Their hatred and fear of the establishment of the Jewish National Home.
'We make the following comments on these two causes:
"(i) They were the same underlying causes as those which brought about the 'disturbances' of 1920, 1921, 1929 and 1933.
"(ii) They were, and always have been, inextricably linked together. The Balfour Declaration and the Mandate under which it was to be implemented involved the denial of national independence at the outset. The subsequent growth of the national home created a practical obstacle, and the only serious one, to the concession later of national independence. It was believed that its further growth might mean the political as well as economic subjection of the Arabs to the Jews, so that if, ultimately, the Mandate should terminate and Palestine become independent, it would not be a national independence in the Arab sense but self-government by a Jewish majority.
"(iii) They were the only 'underlying' causes. All the other factors were complementary or subsidiary, aggravating the two causes or helping to determine the time at which the disturbances broke out."
On the new Arab hostility towards the Jews:
"... It is indeed, one of the most unhappy aspects of the present situation - this opening of a breach between Jewry and the Arab world. We believe that not in Palestine only but in all the Middle East the Arabs might profit from the capital and enterprise which the Jews are ready enough to provide; and we believe that in ordinary circumstances the various Arab Governments would be ready enough on their side to permit a measure of Jewish immigration under their own conditions and control. But the creation of the national home has been neither conditioned nor controlled by the Arabs of Palestine. It has been established directly against their will. And that hard fact has had its natural reaction on Arab minds elsewhere. The Jews were fully entitled to enter the door forced open for them into Palestine. They did it with the sanction and encouragement of the League of Nations and the United States of America. But by doing it they have closed the other doors of the Arab World against them. And in certain circumstances this antagonism might become dangerously aggressive."
SOURCE: - See more at:
The Origins and Evolution of the Palestine Problem - CEIRPP, DPR study, part I: 1917-1947 (30 June 1978)