The road to political stability was difficult for the countries of southern europe due to a
lack of a cultural identity.
long history of invasions.
lack of key trade routes.
series of failed governments.

series of failed governments

Explanation:

The countries of Southern Europe, such as Spain, Italy, and Greece, were anything but stable. The reason for this was that they had very bad governments which were not able to keep the countries united, nor did they provided economic prosperity. Despite them having different routes, with Spain being united for a lot of time, but was a declining power, Italy has just united, and Greece got out of the Ottoman Empire, the manner in which they functioned was pretty much the same. In all of them, there were several revolutions, and finally after some time the situation managed to stabilize and these countries were set on the right track in the middle of the 20th century.

"Series of failed governments", is the best option  to choose from the given options.

Explanation:

More rescission Crises after Second World War: