During the Spanish era Rondalya music, where traditional string orchestra mandolin type instruments were used, was widespread. Kundiman developed in the 1920s and 30's, and had a renaissance in the postwar period. The American colonial period exposed many Filipinos to US culture and popular forms of music. Rock music was introduced to Filipinos in the 1960s, and developed into Filipino rock, or "Pinoy rock", a term encompassing diverse styles such as pop rock, alternative rock, heavy metal, punk, new wave, ska, and reggae. Martial law in the 1970s produced several Filipino folk rock bands and artists who were at the forefront of political demonstrations. The 1970s also saw the birth of Manila Sound and Original Pilipino Music (OPM). Filipino hip-hop traces its origins back to 1979, entering the mainstream in 1990. Karaoke is a popular activity in the country. From 2010 to 2020, Philippine pop music or P-pop went through a huge metamorphosis in its increased quality, budget, investment, and variety, matching the country's rapid economic growth, and an accompanying social and cultural resurgence of its Asian identity. This was heard by heavy influence from K-pop and J-pop, growth in Asian style ballads, idol groups, and EDM music, and less reliance on Western genres, mirroring the Korean wave and similar Japanese wave popularity among millennial Filipinos and mainstream culture.