City pop is a loosely defined genre of western-inspired Japanese pop that emerged in the late 70s and 80s. Bands like Happy End and Sugar Babe paved the way for city pop with Happy End’s folky sound and Sugar Babe’s American soft rock inspired music.
These bands would break up not long after forming but the members would become integral to the genre in their solo careers. The style of City Pop took from disco, jazz fusion, funk, R&B, soft rock, Latin, and Caribbean music and would incorporate English words.
Japan’s thriving economy and technology boom had a major influence as well, particularly cars with built-in stereos and walkmans. The tech fueled sound would be listened to on joyrides and walks and became the soundtrack for the leisure lifestyle at the time.
The songs all have a nostalgic feel to them for a more hopeful time in Japan before the economic crash they are still feeling to this day. This style of music fell out of favor as the Japanese people that listened to it grew up and stopped relating to the care free lyrics. 
City Pop had a resurgence in the 2010s when the songs would circulate on YouTube with clips of anime. This helped the genre spread to America and gain appreciation. 

夏なんです – Happy End
アフリカへ行きたい – Yumi Arai
4:00A.M. – Taeko Onuki
少女A – Akina Nakamori