Father in Berlin is entertaining American artist (7)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

DAD (Father) A (American) IST (German for ‘is’ i.e. in Berlin) . Heavily influenced by WWI, DADAISTs rejected violence, war, nationalism and modern capitalist society, using nonsense and protest in their works. The whole point behind Dadaism was to prove that anything could be art if the artist declared it to be, which in turn proved that if everything could be art, then nothing could be art. This outraged many artists as Dadaism deemed their labour-intensive artworks meaningless.