New development was the Tsar's involvement in the War. The victorious spring triggered the Court to seek his help, however for the lack of precise information quite a few people (among them the Peace Party, and maybe Görgey, or even the members of the government) thought it was a reaction for the declaration of independence. The news arrived spring, the armies summer.
The plan was to face the Kaiser's and try diplomacy against the Tsar's. After the battles in the west didn't produce the results fast enough, the government decided to concentrate the armies near Szeged (in the south on the Great Plain) which was a silly plan since that allowed Haynau and Paskevich to join forces. Btw Haynau (the Hyena), he was freshly appointed to lead the imperial troops on Hungarian lands, after he was recalled from his Italian holiday mayhem. He was a tougher nut than Windisch-Grätz.
Görgey commuted between Pest and Komárom which served as the main base for the western operations. His division between his two office hindered him to serve optimally, finally his appointment as a minister was revoked (thanks for a mixup), he got a headwound which incapacitated him for a while, and they had to give up Transdanubia according to the new plan. They were late and a Russian unit stood already in their way. They had to evade which made their trip longer, and Russian envoys approached him but apparently they were just distractions to grant time for an encirclement. Görgey didn't let his army getting trapped but himself sent messages to Paskevich, in word and in letter. He prodded the Russian leadership if we could capitulate to them, and what would they think if they could place a Russian ruler above our country. Problem was he didn't have the authority to parley and the government didn't know about his diplomatic actions, they were informed after the fact.
Our armies had no time to unite. The main force was led instead of Arad to Temesvár by Dembinski, the place was in the hand of the enemy, and he managed to send the baggage train with the supplies elsewhere. For his failure he gave up the command, and Bem was trusted with that, he couldn't do much but went to battle against Haynau on the 9th of August, and our army got destroyed. Görgey stood at Arad where the same day he had a meeting with Kossuth. Kossuth reproached Görgey, but essentially they discussed the case if we lose the battle, Görgey raised the possibility of the capitulation.
Few hours later when the news arrived Görgey went to Kossuth and asked to give him the power, the Russians did't negotiate with the revolutionary government, only with the military. Kossuth resigned and Görgey assumed dictatorship. On 13th August at Világos he laid down the arms in front of a Russian general, Rüdiger.