How did Palestine change in the 1920s?
it became split between jews and arabs
Jews first fought for Palestine in the Biblical Period (around 1000 BCE). Muslims first fought for Palestine in 634 CE. If the question means to ask when they first fought each other for Palestine, there were pogroms and violent outbursts between Jews of the Yishuv and Settled Arabs of Palestine as early as the later 1920s.
There was no genocide in Palestine. This is hyperbole. The actual Israeli-Palestinian Conflict has been going on since the 1920s or late 1940s depending on how you define the groups. To read more about why Palestine is not a genocide or how the Israeli-Palestinian Conflict began, please see the Related Questions below.