Christianity did not easily spread through the Roman Empire.
See the related question, "How did Christianity spread throughout the Roman Empire?"
No religion helped to save Roman culture. One religion spread through the Roman Empire in its later days and transformed Roman culture: Christianity.
The Romans spread two different religions: pagan religion and Catholicism. In the early days of the Roman empire, they spread pagan Roman religion that is usually referred today as Roman Mythology. In 312 AD, Emperor Constantine converted to Catholicism, and made it the state religion in 313. After that point Catholicism was spread by the sword across the Roman Empire. This practice continued until the fall of the Roman Empire, and was picked up by most of the kingdoms that rose out of that collapse. The general way of spreading religion within the Roman Empire, and even more so by the governments that followed the fall of the Roman Empire, was if you did not convert to Catholicism, you died.
No religion "inspired" the Ottoman Empire. The Ottoman Empire had Sunni Islam as its State Religion, but it was not a view or tenet of Islam to create an Ottoman Empire.
It was Jesus Christ via the missionary work of the apostles. Christianity was the monotheistic religion which spread in the Roman Empire.
Please specify which new religion you are referring to. several new religions spread in the roman Empire
It was Chrisitanity
Through most of their history the ancient Romans had their own religion: Roman Religion. In the Later Empire Christianity spread in the Roman Empire, was endorsed by the Roman emperors and became state religion.
That would be Christianity.
Christianity
Charlemagne helped spread Christianity throughout the Frankish Empire and the lands he conquered. He spread Christianity through both peaceful conversion efforts and military conquests.
No religion helped to save Roman culture. One religion spread through the Roman Empire in its later days and transformed Roman culture: Christianity.
Catholicism
What religion spread from North Africa to west Africa
There are two "Islams". The first is the religion which spread primarily through peaceful interaction or the benefits it provided under the stewardship of an Islamic State. The second Islam was an actual Empire or Islamic State which expanded through warfare and conquest. It is necessary to understand that while the Islamic Empire grew through warfare, most conversions to Islam were not compelled.
The Songhai Empire contributed to the spread of Islam and Arabic through trade and contact with Arab merchants, scholars, and traders. As the empire grew in wealth and power, it attracted Muslim scholars and traders who spread their religion and language through interactions with the local population. Additionally, the ruling elite of the Songhai Empire embraced Islam, further promoting its spread among the populace.
The Roman Empire.
Ashoka was important because he spread Buddhist religion to his empire.