At this time, on the initiative of Emperor Rudolph II a final attempt was made to attain a general peace between Philip and the States-General in the German city of Cologne. As both sides insisted on mutually exclusive demands these peace talks only served to make the irreconcilability of both parties obvious; there appeared to be no more room for the people who favoured the middle ground, like Count Rennenberg. Rennenberg, a Catholic, now made up his mind to go over to Spain. In March 1580 he called for the provinces in his remit to rise against the "tyranny" of Holland and the Protestants. However, this only served to unleash an anti-Catholic backlash in Friesland and Overijssel. The States of Overijssel were finally convinced to adhere to the Union of Utrecht. Nevertheless, Rennenberg's "treason" posed a severe strategic threat for the Union, especially after Parma sent him reinforcements in June. He managed to capture most of Groningen, Drenthe, and Overijssel in the next months.