Query: With what country did Libya conclude the Hassi Messaoud defense agreement?
Context: Retaliating, Gaddafi sponsored anti-government militants in Tunisia into the 1980s. Turning his attention to Algeria, in 1975 Libya signed the Hassi Messaoud defence agreement allegedly to counter "Moroccan expansionism", also funding the Polisario Front of Western Sahara in their independence struggle against Morocco. Seeking to diversify Libya's economy, Gaddafi's government began purchasing shares in major European corporations like Fiat as well as buying real estate in Malta and Italy, which would become a valuable source of income during the 1980s oil slump.