Settlement in Palestine may have started in 1882, but Zionism didn't really develop as a political movement until 1896. Theodor Herzl, a Western European Jew who was once committed to the assimilation movement, turned Zionism from an idea into a mass movement, a political force. He was against the slow settlement of Jews in Palestine, and worked instead towards political autonomy. His was a diplomatic battle: his targets, world leaders outside Palestine.
Herzl's diplomatic battle wasn't just directed at heads of state – he struggled to convince most Jews in Western and Central Europe to support political Zionism. Many of them were focused on emancipation (civil rights) and assimilation and believed that their work would be impeded if Jews asserted a national identity. (These assimilationists were also threatened by the well-known participation of Jews in revolutionary organizations in Russia. Those Jews seemed to "prove" the anti-Semitic notion that Jews everywhere were "the enemy of order and the subverter of society"). Zionism spread much more successfully in Russia and Poland, where anti-Semitism was more of a physical threat.
Herzl tried to make political allies wherever he could. The Russian government was interested in improving their public image in Western Europe following those nasty pogroms. They gave material support to the Zionist movement, in part also hoping to encourage Jews to leave Russia, where they weren't particularly wanted. From the start, the Zionist movement had strange bedfellows, to say the least . . .
The Zionist movement went for decades without a diplomatic success. When the First World War began, it offered opportunity for shifts in world public opinion. The Zionist movement jumped on this. Zionists from both Allied and Axis countries tried to steer their leaders towards support for the movement. In Britain, Palestine was considered strategic territory for the future "security" of the Empire. The government wanted a way to control that land. Government officials were divided on how this could best be accomplished – the strategy of supporting Zionism won. Chaim Weizman, a Zionist leader from Britain, secured the Balfour Declaration in 1917, which supported the establishment of a Jewish "national home" without explicitly mentioning a state. It was good enough for the Zionists for the time being.
There were, however, two other promises the British government made simultaneously, and all of them conflicted. The British government signed on to the Sykes-Picot Agreement with France – which basically divided the Middle East into areas of British and French control. They had also put forth and the McMahon-Hussein correspondence – in which the British High Commissioner of Egypt made a deal with Sherif Hussian of Mecca to recognize Arab independence in return for Allied support during an important battle. Today, we are still seeing the fallout of the double-crossing, or rather, triple-crossing, of the British government.