What sorts of solutions or justifications did Christianity implement to eradicate this problem? 

• One primary strategy was to portray Islamic figures as outside of the time period, and not within the confines of modernity of the time. If a group had no history, they had nothing. The Christian Church made sure this was true for Islam attempting to do so by steadily erasing narratives put forth from Islamic people with their own fabrications or exaggerations. The act of encasing Islamdom in ambivalence put them in a more vulnerable position to have their weaknesses exposed and exploited.
• Upon the introduction of these two religions, they were each completely new to one another, and this unfamiliarity manifested as danger. The Islam world was unknowable and undefinable at this point through a Christian perspective, and that inspired fear throughout the Occident, and consequently an urgency to conquer that fear, one way or another. One vocabulary word to remember as you explore this site is "Saracen," which was a derogatory term created to represent Islamic people in the medieval ages, and simply the title on its own grew to inspire this intense sense of fear that white Christians felt towards them.