Well, sure, there was violence before 1948, but that's not the same thing as conflict in terms of international armed conflict which is what the Israeli-Palestinian conflict really is.
The following excerpts have been taken from the United Nations website:
www.un.org/unispal/history/
"Palestine was among former Ottoman territories placed under UK administration by the League of Nations in 1922. "
You can see in this link which countries were members of the League Of Nations in 1922 when Palestine was placed under UK administration.
www.britannica.com/topic/League-of-Nations/Members-of-the-League-of-Nations
"UK considered various formulas to bring independence to a land ravaged by violence. In 1947, the UK turned the Palestine problem over to the UN."
Under British administration, Palestine was NOT partitioned, but you will often hear people talking as though it was!
So, we move on to the actual partition itself:
"After looking at alternatives, the UN proposed terminating the Mandate and partitioning Palestine into two independent States, one Palestinian Arab and the other Jewish, with Jerusalem internationalized (Resolution 181 (II) of 1947)."
As we can see, the partition of Palestine was not caused by the British Government alone.
The collective members of the United Nations made that decision.
"One of the two envisaged States proclaimed its independence as Israel and in the 1948 war involving neighbouring Arab States expanded to 77 percent of the territory of mandate Palestine, including the larger part of Jerusalem. "
The Office Of The Historian in the United States says the following:
"The Arab-Israeli War of 1948 broke out when five Arab nations invaded territory in the former Palestinian mandate immediately following the announcement of the independence of the state of Israel on May 14, 1948."
history.state.gov/milestones/1945-1952/arab-israeli-war
Partition was a United Nations collective plan.
Personally, I would argue it was the FIVE Arab States who kickstarted the Arab-Israeli aka Israeli-Palestinian conflict. That kind of warfare was new and arose out of the partition into Israel and Palestine.