The countries of  Turkey, Syria, Iraq, Israel, Egypt, Saudi Arabia, Iran, Oman, Yemen, Afghanistan, Pakistan, Azerbaijan, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan, Bangladesh, Malaysia, and Indonesia.  and also in North Africa: Morocco,  Tunisia, Libya, Egypt, Sudan, as far west as Algeria. And the East coast of  Africa, almost to the horn of Africa. At its height it included most of southeastern Europe to the gates of Vienna, including modern Hungary, Serbia, Bosnia, Romania, Greece, and the Ukraine.  They had invaded the countries between the Black Sea and the Mediterranean including Spain.  Spain was recaptured by Christian kingdoms in the 13th and 14th century although it is 90% Muslim today.

(The history of the Ottoman Empire [the last phase of the Islamic Empire] is one of almost constant warfare. The conflict in Bosnia-Herzegovina, Serbia, and Croatia today is the result of past conflict with the Muslim Turks. Those regions were probably 100% Christian for over 1,000 years, but when the Turks (Islam) invaded they imported Muslim peoples to settle the regions. As you can see the boarders of this old empire is where we see fighting between Christians and Muslims today, as this old empire beings to stretch and flex after a long sleep.)

The only thing that kept Islam out of Europe was the Holy Roman Empire. God's strength against this anti-Christian empire.

Map 1500 AD