The Blue Rider – Der Blaue Reiter – was the name of a group, an almanac and an artistic movement, all of them centred round the remarkable figure of Wassily Kandinsky in the years just before the First World War.

He and the Bavarian Franz Marc together edited the almanac with a Blue Rider on the cover (for Kandinsky, blue meant the spiritual and the bluer the better). But the Blaue Reiter circle as a group was much larger and quite extraordinarily diverse.

There was Gabriele Munter, who in this exhibition takes pride of place with Kandinsky at the centre of the movement; there was the American Robert Delaunay, the Croatian Erma Bossi, the Russian aristocrat Alexaj Jawlensky, the German Maria Frank Marck, wife of Franz.

Tate Modern's "Expressionists, Kandinsky, Münter and The Blue Rider" exhibition identifies 17 artists from a remarkably diverse range of backgrounds and nationalities, who are united in…What? you are left wondering as you explore the over 130 works, brought together in the UK for the first time in over 60 years thanks to a collaboration with the Lenbachhaus art museum in Munich.

They came together, Tate Modern tells us, to form, in their own words, "a union of various countries to serve one purpose" – to transform modern art. It's a punchy notion, and sounds good. But was such a lofty endeavour what really untied and motivated those involved?