They're not. And that is not what their initial intention was.
The events that led to the war in which Jews took over Palestinian lands (in 1948) was more of a "self-fulfilling prophecy": Arabs began to spread rumors (in the 1920s) that Jews want to take over all the land and rule over Arabs. This led Arabs to start massacring Jews, which in turn led Jews to establish militias to protect themselves. Which then spiraled into an Arab-Jewish war in which Jews took over many Palestinian territories.
The initial intention was to
legally buy swamp lands, and abandoned lands in Palestine, cultivate these lands, and bring Jewish immigrants from Europe to settle on these lands, and to
eventually have a democracy with equal rights to Jews and Arabs.
At the time (1900s) there were about 500,000 Arabs in Palestine. You would think this is a large population, but in fact it was relatively small compared to what the land could sustain. The problem was that at the time the land could
not sustain many more people. So the Zionist idea was to drain swamps, and introduce advanced agricultural techniques so the land could sustain many more people.
While the Arab population was 500,000 in Palestine, there were 9 million+ Jews in Europe (this was before the Holocaust). These Jews lived in Europe as refugees or third-class citizens for hundreds of years (I think the holocaust made it quite evident how poorly Jews were treated in Europe). but in any case, this treatment made them desire to return to the land from which they were forced out around 135AD.
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