The histrography and definition of Zionism is a complex topic, made up of many layers and developing over time (Selwyn, 1993). But in summary Zionism is about the establishment of a Jewish community in the land of Israel. It is both a positive ideology, emphasising the cultural goodness of Judaism plus an appeciation of the long history of Jewish people, but it's also a reactive ideology, its a response to the global history of anti-semitism. Herzel has his eye on both themes when he organized the Zionist movement at the turn of the 20th Century (Avineri, 1998).
References
Abdul-Wahab Kayyali, 'Zionism and Imperialism: The Historical Origins', Journal of Palestine Studies , Spring, 1977, Vol. 6, No. 3 (Spring, 1977), pp. 98-112.
Ruth and Tom Selwyn, 'Zionism', European Judaism: A Journal for the New Europe, Vol. 26, No. 1 (Spring 93), pp. 28-34.
Shlomo Avineri, 'Herzl's Road to Zionism' The American Jewish Year Book, Vol. 98 (1998), pp. 3-15.
Walter Laqueur and Barry rubin, eds. The Israel-Arab Reader: A documentary History of the Middle East Conflict, London: Penguin Books, 2008.