Answer:
The Byzantine Emperor sought the crusaders' help to defeat the Arab Muslims.
Western countries launched a series of crusades.
The fourth crusade attacked and sacked the city of Constantinople.
The Ottoman Turks conquered Constantinople.
Explanation:
The Crusaders were a group of fighting men who are to help fight against the Muslims and get back the Holy Land from their rule.
In <u>1095, the Byzantine Emperor Alexios I Komnenos requested military assistance from the Crusaders to help him defeat the Arab Muslims</u>. The Muslim Seljuk Turks' main objective was to capture Constantinople. So, the need to defend the city was a much-needed act.
Then this was followed by several <u>western countries launching crusades</u> of their own. This was the start of the very First Crusade in <u>1096</u>.
Later on, the <u>Fourth Crusade led by Pope Innocent III attacked and sacked the city of Constantinople instead of the planned attack on Egypt in 1204</u>. This was a new turn of events in the history of the Crusades, for it shows the fight as not between Christians and Muslims as was the intention but rather between Christians themselves.
This then eventually led to the <u>Ottoman Turks conquered the city of Constantinople in 6 April 1453</u> when Mehmed II led his army and made Constantinople the capital of the Ottoman empire.