BRATISLAVA, Slovakia — As Europe struggles to keep Greece from default and to hold its common currency together, violent protests against immigration in Slovakia and election results in Denmark over the weekend have strengthened the forces of disunion unleashed by an impassioned debate over how to deal with a flood of migrants from conflict zones.

The protests here in Bratislava, organized by an extremist outfit called Stop the Islamization of Europe, ended with more than 100 arrests on Saturday. They played out just two days after the anti-immigration Danish People’s Party, once dismissed as an assembly of marginal cranks, won more than 20 percent of the vote in parliamentary elections in Denmark.

The events in Slovakia and Denmark, both members of the European Union, added to a sense of disarray in the 28-nation bloc as it simultaneously grapples with two severe crises: a wave of desperate migrants fleeing war and poverty, and the prospect that Greece may default on loan payments due at the end of the month and even leave the group of 19 countries that use the euro.

The anti-immigrant protests here in Slovakia’s capital took place as regional leaders and security analysts gathered in the city for a conference focused on yet another concern for Europe: the security threat posed by a resurgent Russia. In its response to Russia’s annexation of Crimea last year, however, Europe has managed to maintain a degree of unity, and on Monday it will ratify a six-month extension of sanctions, diplomats in Brussels said.