Under the Ottoman empire, the Christians, Muslims and Jews lived together peacefully, more or less. There were no conflicts. One reason behind it can be that most of the land was empty. There were very few settlements on the land. And the population was very little in the area.
Now we fast forward to the year 1915. World War 1 began. The British, French and Arab revolutionaries were fighting the Ottoman empire. The British play a clever hand here. They tell the Arab revolutionaries that in return for their support in defeating the Ottoman empire, they will give them the Palestine area. And the Arab revolutionaries were fighting to create a unified Arab country. The Arab Revolutionaries wanted one Arab country from Syria to Yemen.
The Britishers promise the same thing to the Jews. That they will help them to create their own Jewish country near Palestine. Why do they do this? So that they could appease the American Jews. And could gain influence on American politics.