Italy has over hundreds of years been a very important world power. From the Roman empire to the Renaissance and the Age of Exploration, Italy was always a key player in world politics but by WWII it was the least significant of the Axis powers and several of its neighbors had overtaken it in power. What happened between ~ 1600 to 1900 to cause Italy to diminish in status?
A reply to /u/DtownMaverick
I don't know if you are aware, but Italy as we know it today didn't exist as a country until the modern Kingdom of Italy was founded in 1861 following the risorgimento movement. Prior to that it was a collection of territories and powers, many of which were under foreign lordship.
There was a theoretical Kingdom of Italy under the Holy Roman Empire, but it was exactly that: a theoretical crown.
In 1600 Italy was mostly controlled by the King of Spain either directly or indirectly, following failed French attempts in the Italian Wars culminating in the treaty of Cateau-Cambresis in 1559.
There was the Duchy of Milan, powerful and under direct Habsburg control with Philip III of Spain as the Duke of Milan following his father Philip II of Spain the first Habsburg Duke of Milan. There was the Kingdom of Naples which came to Habsburg possession through the Aragonese Trastamara. There was the Duchy of Parma, created by Charles V and consistently allied with the Habsburgs. There was the Republic of Genoa, who shifted from her French orbit in the late medieval era into a reliable ally of the Spanish in the early modern era. There was her rival Venice which was in slow decline. And of course, the Papal States. But there was no "Italy". There was not even much of a notable interest in "Italy" as the period under the Habsburg monarchy was a notably peaceful and prosperous time.
When people say "Italy" was a major contributor to the Renaissance, age of exploration, etc. what is meant is that people from Italy and/or Italian states were contributors. There was no Italian nation.