ROME (AP) — Italy's president has recalled World War I's roots in "aggressive nationalism" and urged young people to remember the conflict's lessons while striving for peaceful co-existence.

Italian head of state Sergio Mattarella attended several ceremonies in Italy on Sunday, part of a week of observances marking the 100th anniversary of the war's end.

One was in Trieste, an Adriatic port not far from some of the final, deadliest battles between Italian soldiers and troops of the Austrian-Hungarian empire.

Mattarella said the war demonstrated the "incapacity of the European ruling class" to pursue "national aspirations and interests in a peaceful" way and surrender to "aggressive nationalism" and quests for power.

Mattarella said an "active" memory for the victims of wars can shore up freedom and peaceful co-existence as "irreversible" choices for Europeans.