There is a list of library databases below that will have quality information about different topics for the musicology assignment.
Keep in mind that each decade in the last century has has a strong musical soundtrack. Ragtime music was popular during the 1910's. The 1920's was known as the Jazz Age and blues and Broadway music were also popular. The 1940's had big band music and singers often tried to keep upbeat while supplying the soundtrack to WWII. The 1950's ushered in rock 'n roll, country and rhythm & blues. The 1960's had protest, surf and psychedelic music, not to mention the British Invasion and Motown. The 1970's was known for folk, funk, disco, punk and classic rock. The 1980's had electronic music, hair bands, new wave, and rap/hip hop. The early 1990's introduced the world to Grunge.
All of these musical styles were born out of the social, political, and economic events happening in those decades.Consider a style of music, or a specific song to write about for this assignment. Use the library databases to research what was going on in the background. If someone were to write about the 1960's, it would be good to research the political and social events of that time. For example, use the search term '1960s protest songs' in the library database ProQuest Central.