1. Google “EU TERRORISM SITUATION AND TREND REPORT”
2. Enter the official Europol page, with the latest report (currently 2014 report, showing 2013 events, compared to 2012 events) https://www.europol.europa.eu/sites/default/files/publications/europol_tsat14_web_1.pdf
3. Read the table and comments in ANNEX 1: OVERVIEW OF THE FAILED, FOILED AND COMPLETED ATTACKS IN 2013 PER EU MEMBER STATE AND PER AFFILIATION.
4. Add some spice, reading the rest of annexes.
5. Repeat for similar reports back in time.
6. PROFIT! (Due to the increase of knowledge)
Quick link (also some US-related info): http://www.loonwatch.com/2010/01/terrorism-in-europe/