Complex sentence: Because this party wanted to make its own socialist and Marxist ideas clear, it decided to change the colour of the star to red; in 1969, this new version of the "estelada" started to appear at PSAN meetings.
Split into simpler sentences: Because this party wanted to make its own socialist and Marxist ideas clear, it decided to change the colour of the star to red. So, in 1969, a new version of the estelada started to appear at PSAN meetings.