Hi Conus Lotus
Is Roman Catholicism the same thing as Christianity? you ask...
The strict answer is no. Roman Catholocism is a christian faith. Christianity encompasses all faiths that profess Jesus as Christ, the son of God. Hence, christ- ianity.
"Catholic" is from its close hebrew word meaning "universal". Men being men, a first shism occured after a couple/few hundred years when the Catholic orthodox church first came into being with its own head of church. JP II made some memorable amends with them during his pontificat.
Not knowing all of others, I remember Luther's 96 "arguments" in the early second quarter of the1500s which started the Lutheran church.
I always get the Anglican church's debut and Protestant church's mixed up. The latter, I believe, came about after Ann Bolyn (bad spelling?) 's not bearing a son for good old Henry the 8th. The king seperated from the Catholic church to permit, and justify, his divorce/seperation so he could wed someone else... to bear him a son. That be the Protestant church. The Anglican church has a High Anglican church and a Low Anglican church. The latter, I believe, is the closest in doctrine to the catholic church.
The Baptist church is also another "christian" church.
There are strict rules about recongnizing "churches" as being christian. I only know about that without knowing what they all are, but believing in Jesus, the Christ, is one of them.
Word came out of Australia about a month or less ago about "talks" between the protestant church and the "catholic" church to "reunite". The catholic bishop that was quoted in the article insisted that they were only talks.
But there is a strong euchumenical movement, at least here in Canada. A coming together of all these denominations of christianity in worship. The hope is to create greater ties.