Christianity starts out thinking of itself as Judaism fulfilled– a community mostly consisting of Jews and Gentiles already sympathetic to Judaism who together proclaimed Jesus as the fulfillment of the prophetic promises of a messiah.
As persecution broke out, particularly after the Jewish revolt against Rome, Christianity and Judaism part ways.
In response to charges of being a group of nutters from many Roman onlookers, Christianity began to adopt more Greco-Roman philosophy (moving away from its Hebraic roots) to explain its doctrines.
This eventually results in the emergence of Orthodox Christian theology.
First, however, resulted in the rise of many heresies. In response to these heresies, the Church developed a body of tradition (there wasn’t really a clear view on a canon of scripture yet) that becomes the Ecumenical Creeds (Apostle’s Creed, Nicene Creed, etc). These creeds become the cornerstone of Christian Orthodoxy, written to denounce heretical views and provide a basic core of doctrines that all Christians were expected to believe (including statements about the Trinity, the deity and humanity of Christ, the incarnation, resurrection, ascension and return, etc.).
There is also a strong sense of catholicity in the creeds: one of the primary defenses against heresy is the declaration that all churches hold these doctrines, so heretics are proven wrong by their going against what the whole Church teaches.
This united sense of catholicity doesn’t last for very long. Eventually East and West split. Then, in the West, the Reformation causes even more fracturing.
The Reformers reacted against a Roman Church that saw itself as the source of true doctrine, and so they emphasized the idea of sola scriptura: scripture alone is the source of true doctrine.
However, scripture has to be interpreted for us to understand it, and this to some extend depends on philosophy, tradition, and other similar factors. This results in a lot of division among Protestants.
After the Enlightenment, many Protestants adopt a Higher Critical view of the scriptures.
In response to this arises Fundamentalism, a conservative movement based around sets of fundamental beliefs considered necessary to be true to the faith. Fundamentalism got laughed out of the academic world, succumbed to internal divisions, and became ultimately ineffective as a counter-movment to “liberal” Christianity.
As an attempt to overcome the failures of Fundamentalism, the contemporary Evangelical movement emerged in the second half of the twentieth century. Still essentially conservative in nature, this movement more intentionally engaged with modern philosophy and science and allowed for a wider diversity of belief within its own ranks.
This is, of course, a vastly oversimplified history. I’ve mainly focused on different views regarding the authority and source of theology, leaving specific doctrinal differences alone. This is also being done from the perspective of a contemporary evangelical, limiting its perspective and leaving a whole world of thought untouched. All of that will have to wait for another time.