As discussed in our article about the Die Brücke movement, this painting captures several members of this influential group that would become a significant part of the overall direction of German Expressionism. Ernst Ludwig Kirchner, Otto Mueller, Erich Heckel and Karl Schmidt-Rottluff are the figures in this multiple portrait and, other than Mueller, they were integral to the early years of this forward-thinking group. It is true that over the years that they spent together cracks would start to show in their relationships with each other, though this is hardly unusual for friendships between creative people.
Any group of artists or musicians will likely over time develop different ideas over the preferred direction of the overall movement, see the many musicial groups who have split up after several years together, for example. Painters and sculptors are also known for being particularly passioniate about their work and forthright in their opinions about what the best approach would be, with a stubborness to follow another artist's direction. More on Kirchner's own opinions can be found in this list of his quotes. Other related artists that you may also be interested include August Macke, Edvard Munch and Fernand Leger.
The Museum Ludwig in Cologne currently owns this piece and also has a number of other artworks of great significance within the overall sphere of German and European art. They specialise in relatively modern art, including Pop Art, Surrealism and also other forms of Abstract art. The Sammlung Haubrich was a large collection of art related to the work of Kirchner that was gifted to this institution and includes many of their highlights, though other pieces have come from alternative sources too. Erich Heckel, Karl Schmidt-Rottluff, Ernst Ludwig Kirchner, August Macke and Otto Mueller are all featured extensively here, making it a must-visit venue for those interested in the merits of the German Expressionists.