The arrest came about in the context of a wave of strikes across the country, triggered by intensifying economic hardship. Iwan Katz delivered a speech in Hannover which was believed by the authorities to have caused or contributed to serious street disturbances. It is not clear how long he was detained. More serious and sustained street disturbances erupted in Hamburg a couple of months later, over three days towards the end of October 1923. The so-called Hamburg Uprising was deemed a failure for the Communist Party. It frightened the government, which outlawed the party (to little obvious effect) for several months. But a spontaneous German re-run of Russia's 1917 "October revolution", after which many of the more radical comrades yearned, failed to materialise. Political divisions on the political left, most obviously between the Communist Party and the centre-left SPD were intensified, and among the Communist party leaders the more extreme pro-Moscow factions strengthened their position following the fall from favour of the party leadership team of Heinrich Brandler and August Thalheimer, both of whom found themselves invited to relocate to Moscow in January 1924. A new leadership collective emerged for the party in Germany, which included the charismatic Ernst Thälmann, a staunch Stalin ally. Iwan Katz also found himself a member of the party leadership team at a national level. At the 9th party congress, which took place in April 1924, and was held that year in Frankfurt am Main, Iwan Katz was elected to the fifteen member . Within it, he also joined the party politburo.