Anybody who disbelieves that the Republic of Ireland did not successfully use terrorism in the Irish War of Independence (1919 - 1921) really does need to do some serious research into the matter. Furthermore, they would not have to look very hard, either! The result of this first campaign by the IRA was the Anglo-Irish Treaty of December 1921, which removed 26 counties of Ireland from British Rule.
That terrorist campaign took place 50 years before the Provisional IRA's failed attempt (1969-1998) to unite the six counties of Ulster with the Irish Republic.
As with Ireland, also with Israel, the evidence is very easy to find regarding its use of terrorism. Most recently, the American Jewish academic, Richard Falk, described the foundation of Israel as the "most successful terrorist campaign in history." Another informative read is Bruce Hoffman's Israel: The Original Terrorist State.
On the 1st October 1948, the newly appointed UN Commissioner to Palestine, Ralph Bunche, was presented with a report which listed all known acts of Jewish terrorism that had occurred over the previous four years. These began on the 6th November 1944, with the assassination of the British Resident Minister in the Middle East, Lord Moyne. These ended on the 17th September 1948, with the assassination of Ralph Bunche's predecessor, the United Nations Mediator for Palestine, Count Folke Bernadotte. There was a total of 259 incidents of terrorism on that list.
It is generally agreed that the "Jewish Insurrection", as it is sometimes referred to as, had the effect of making "the cost of occupation too high" for a nearly bankrupt Britain. That led to a British evacuation of the territory in May of 1948, thus leaving the problem to the United Nations.
You certainly do not have to be a Major in History to uncover this information!