Complex sentence: After the "Tonkünstler-Versammlung" of 1861 in Weimar, there was a break until 1864, when in Karlsruhe the next meeting took place.
Split into simpler sentences: After the "Tonkünstler-Versammlung" of 1861 in Weimar, there was a break of three years. In 1864, in Karlsruhe, the next "Tonkünstler-Versammlung" took place.