Many Palestinian terror groups were formed, such as Hamas and Hezbollah.
Hamas inparticular, to achieve their goals, would use bombs in Israel, capture and torture politicians and attempt assassinations, causing the IDF (Israeli Defence Force) to retaliate, eventually killing their leaders.
This slowed the peace process dramatically, due to the nonrecognition of Israel being their own country by Palestine terror groups.
Although, there are groups that were trying to quicken the peace process, such as Fatah, which were eventually disbanded by Hamas.
Hope this helped somehow!