Zionists wanted Jews to have power and in particular, colonial power - like the great empires of Britain and France. Rich Jewish bourgeois were not accepted as equal in Europe and Britain. So they decided to grab enough land and even the whole region, to possess and colonize, to separate themselves from Gentiles and wage their own imperialism. They marketed this enterprise as "empowering Jewish people". Making them "muscular". In reality, it was and is an enterprise of colonial greed of certain group that considers itself special and unlike the rest of humanity.
So the reason behind Zionism was greed for power and riches - supremacism that they were denied in Gentile societies at that time. They wanted power in the open. As a "people".