Mainstream historical events

313 CERoman Emperor Constantine legalized Christianity, which then became the dominant faith in all Roman territories.
The Holy Land (Israel & Palestine), Egypt, and North Africa became strong, vibrant Christian communities.
325 CEFirst Church of Nativity was established in Bethlehem.
Council of Nice (Nicea) met (discussed above)
331 CEConstantine moved the seat of the Roman Empire to Constantinople (Turkey today); which gave more power over the Holy Land to the Eastern Church; from then on, there were strained relations between the Pope’s Western Church out of Rome and the Eastern Church.
614-628 CESassanians (Persians) and 26,000 Jewish soldiers allied to take over the Holy Land; Sassanians wanted a harbor to the Mediterranean Sea and the Jewish wanted the Holy Land. Anywhere from 17,000-60,000 Christians were killed. 
The Eastern Roman Empire soon recaptured the Holy Land (some time between 628-638).
638 CE6 years after the death of Mohammed, Arabian (Islamic) forces took over Jerusalem and Egypt, which began a 94-year-long Islamic westward advancement.
700 CEIslamic forces took over Northern Africa (Roman Africa).
711 CEIslamic forces occupied Spain.
718 CESeries of Christian crusader campaigns occurred in Spain and Portugal to recapture territory from Islamic forces. Oahspe mentions these early crusades as well and says that 7 were killed.
732 CEChristian victory of Charles Martel at Tours and Potier ended the 94-year Islamic advancement westward. Christians still had Constantinople, but were stripped of Syria, Palestine, and Northern Africa.
732-1000 CEOver these 3 centuries, the Roman Empire (Christianity) was able to recover somewhat, but did not reclaim the Holy Land.
By 1000, most of Europe was converted to Christianity
850-1050 CEBetween the Church of the West out of Rome and the Eastern Church, increasingly pronounced differences strained relations.
1054 CEAfter 2 centuries of strained relations, there was a major break-up between the Pope’s Christian Church of the West (Rome) and the Eastern Church, called the schism of 1054, which resulted in the Orthodox churches.
1091-1291 CEAfter the schism of 1054 totally divided the 2 Christian churches, the succeeding Pope(s) of the West tried to mend things by sending Christian crusader armies to help the Eastern Roman Empire defeat their Islamic enemies, but they were just used for their military, their crusader armies also exacerbated resentment towards them, and the division deepened and would not begin to improve until around 1095. 
https://www.catholiceducation.org/en/controversy/common-misconceptions/the-battle-over-the-crusades.html