Before 1914, nationalism in the Balkan Peninsula contributed to the inability of countries to make reparation payments. the inability of countries to make reparation payments. campaigns by foreign diplomats against the use of trench warfare. campaigns by foreign diplomats against the use of trench warfare. the rejection of the Versailles Treaty by combatants. the rejection of the Versailles Treaty by combatants. resistance by ethnic groups to Austrian rule. resistance by ethnic groups to Austrian rule.