I'm not speaking just about the conquest of the Americas, I'm speaking about Europe.
Here is an excerpt and a very basic summary of that period from an entirely secular website which has no Christian cause to advance. If there were pockets of forced conversions that must be the extent of it because they keep alluding to these invading pagan hoardes who converted themselves after they conquered European lands.
How Christianity Rose to Dominate Europe
Upon the collapse of the Western Roman Empire in 476, secular authority broke down throughout the former Roman Empire Western and Central Europe. As invading Germanic tribes took control of former Roman lands, the rule of law became virtually non-existent. The Roman Catholic Church organizational apparatus remained intact though, causing the Christianized masses to look to the Church first and foremost for guidance during this chaotic time. Thus, the power and influence of the Roman Catholic Church continued to grow.
However, other hallmarks of Roman life dwindled, including education. This only served the Catholic Church even more, as it was relied upon for knowledge of the world, as clergy were typically among the rare few that became literate and educated. Naturally, they primarily imparted only faith-promoting religious knowledge, not wanting to distract its congregations from the path to salvation.
The Catholic churches also served as libraries for secular literature, including non-religious philosophical writings, such as those from Greek philosophers. This material was not shared with congregations, becoming largely forgotten during the Dark Ages. Many (perhaps most) of these writings became lost during the Medieval times. Critics accuse the Catholic Church of intentionally purging these non-religious writings, but there is little to no direct evidence of this. Many books were lost due to natural perishability of books, and barbaric raids (such as the Huns), contributing to the Dark Ages by inhibiting illuminating worldly knowledge.
In a very real sense, the Catholic Church became the "information highway" of the Middle Ages, controlling the message dispersed to the masses, and thereby strongly influencing beliefs, attitudes and actions. In addition to "pagan" philosophies, many other fields of knowledge were suppressed, such as science, technology, etc.
The Roman Catholic Church not only controlled the flow of information, but they also had a strong say in secular politics, becoming "kingmakers". Kings that aligned with the Church gained an advantage with the large, Christian populations left behind by the collapse of the Roman Empire.
Most Germanic kings learned this quickly, adopting Christianity soon after conquering former Roman provinces. The Ostrogoths converted after conquering Italy, the Franks converted after conquering Gaul (roughly approximate to modern France), and the Visigoths converted after conquering Hispania (modern Spain and Portugal). Doing so enabled each to consolidate rule in their new kingdoms, gaining support amongst their new subjects.
In addition to lending their approval of a new ruler, the Church also aided kings and rulers in several other ways. For example, monasteries provided public relations support on behalf of the king. In exchange, the Church was given lands, and clergy were appointed to influential positions in the King's court, giving the Church a voice in policy.
The Church helped create laws during the Dark Ages throughout Europe as a result, including forced worship and conversions, increased tithes, and repression of anti-Church influences. Kings also benefited by more advantageous trade partnerships with fellow Christian kingdoms, etc.
