Final answer:
The Beatles' break-up first became evident in 1969, as cultural tides shifted towards more rebellious expressions, with events like Woodstock signaling the change.
Step-by-step explanation:
The break-up of the British rock band The Beatles first became evident in 1969. While they embodied the spirit of suburban youth culture in the mid-1960s, by 1969 the culture had shifted to a more rebellious sentiment, exemplified by events like the Woodstock concert. Signs of the band's unrest and divergence were becoming public, marking the beginning of the end of the iconic group.