I mean failed state like Somalia or Afghanistan
I would say it it nearly impossible for a European country to get to that level of state collapse for a long time (outside of direct civil wars). For a few reasons:
1) European cultures lack tribal identities. In Somalia and Iraq, once federal government fell apart, the tribes took over. In the young men of the tribe then took instructions from the elders of the tribe rather than any edicts by a new government. This makes it much harder to re-establish control. Meanwhile in Europe nothing like this really exists. if a government fell apart, warlords or politicians make take over but won't have the same level of control as a tribal elder. This would make it much easier for a government to re-establish control.
2) Europe is highly urbanised and middle class. This makes the people who just want peace a larger part of the population. If you're a subsistence farmer your country falling apart doesn't affect you that much as long as your farm, village and market are peaceful. The Middle Classes such as entrepreneurs and professions suffer much more from a societal collapse. They have a lot more to loose and their job might depend on national or international markets. They also usually have considerable political power too. This reduces they likelyhood of complete collapse and lessens resistance to a peacekeeping force trying to re-establish control.
3) Nationalism: Countries of Europe have hundreds of years of centralised control or thinking themselves as being together as one nationality. This is unlike Iraq or Somalia which are relatively new states. This lessens the likelyhood of complete collapse (doesn't apply to areas with large minorities such as Spain or UK even potentially Italy & Germany)
I think a country in could get to the level of chaos such as Colombia during the civil war. With large parts outside of government control and constant terrorists attacks. But it would be very very hard to make a country as third world as Somalia or Afghan, the countries are just too rich and urbanised.