1920 - Hatch and Millward indicate that many events in the history of recording in the 1920s can be seen as the birth of the modern pop music industry, including in country, blues and hillbilly music.
1926 - The term "pop song," is first recorded as being used in 1926 in the sense of a piece of music "having popular appeal"
1930 - The first major pop stars as such were the crooners of the 1930s and '40s.
1940 - In the 1940s improved microphone design allowed a more intimate singing style.
1950 - According to Grove Music Online, the term "pop music" "originated in Britain in the mid-1950s as a description for Rock and roll and the new youth music styles that it influenced
1950 - Rock'n'roll brought much more of that, and Elvis Presley became a global star, the biggest of the late 1950s and early 1960s.
1952 - Curiously, pop music charts as such didn't exist until 1952, when the first Top Twenty was recorded.
1950’s - Another technological change was the widespread availability of television in the 1950s; with televised performances, "[p]op stars had to have a visual presence".
1960 - Grove Music Online also states that "... in the early 1960s [the term] ‘pop music’ competed terminologically with Beat music [in England], while in the USA its coverage overlapped (as it still does) with that of ‘rock and roll’."
1960’s - In the 1960s, the introduction of inexpensive, portable transistor radios meant that teenagers could listen to music outside of the home.
1962 - From 1962 until their break up in 1970 The Beatles dominated the charts in Britain and America
1967 - From about 1967 the term was increasingly used in opposition to the term rock music, a division that gave generic significance to both terms.
1975 - The real first pop promo video was actually Bohemian Rhapsody by Queen. The footage of the band playing was from a concert they did, but the effects was done in the back of a lorry trailer whilst on tour
1975 - Queen's groundbreaking promo for their 1975 hit Bohemian Rhapsody has been named the UK's best music video in a survey of music fans. Michael Jackson's Thriller came second in the poll, just ahead of Justin Timberlake's Cry Me A River. Britney Spears' Baby One More Time made only 15th on the list. According to the band's drummer Roger Taylor, the "Bo Rhap" promo was "the first video to be used as a really successful promotional tool".
1980’s - The 1980s proved a moribund decade for pop. Styles came and went, but it was an era short on memorable music. Only Wham! (and later George Michael) emerged as true pop stars
1990’s - The 1990s was the time of boy bands, perhaps the ultimate in manufactured acts. ( East 17, Backstreet Boys, Boyzone, Westlife, A1)
2000’s - Since the year 2000 there's been a dearth of major new stars, relying mostly on established talent. Several younger artists have come and gone, and new styles have briefly emerged, but nothing appears to have gained a major foothold besides modern R&B, which owes little to its soulful predecessor, but a lot to hip-hop - which itself has become a pop style.
The growing popularity of the music video and a change in the broadcasting landscape helped break music TV out of its ghetto via a range of dedicated music channels, led by MTV.
