Beyond their rivalry, Manchester and Liverpool actually had a relationship of mutual hatred

Manchester developed into the UK's largest textile industrial city following the Industrial Revolution.
Manufactured goods produced in Manchester were distributed domestically and exported through the Port of Liverpool, located about 50km away.
Liverpool developed as a megacity that imported raw materials and exported manufactured goods, while Manchester developed as a manufacturing city that relied on Liverpool.
This led to a strong perception in Manchester that "we do all the hard work while Liverpool reaps all the benefits," while Liverpool mocked Manchester, saying, "You should be grateful that we developed into a city that sustains you from a mere rural town."
As Liverpool continuously increased port fees and railway usage fees also kept rising, Manchester decided to execute a long-standing canal project, which met with city-wide opposition to the canal in Liverpool.
However, the central government sided with Manchester for the sake of cost reduction, and the massive Manchester Ship Canal project was realized.
After the canal's completion, the railway connecting Manchester and Liverpool became obsolete, and Liverpool, which had been the largest port city in the UK, plummeted into decline so rapidly it would make Detroit, USA, look insignificant.
Liverpool port workers lost their jobs instantly, and many workers moved across to Manchester, causing Liverpool to turn into a "Gotham City" overnight.
Even today, the Liverpool chant heard at Manchester United's home stadium—"You rats, eat your rats" (which is also the origin of the "dog meat song" regarding Park Ji-sung)—is a song that mocks the dire conditions Liverpool faced back then.
While it is a relatively mild derby now, it used to be a violent match that would set the entire city ablaze.