The Axis puppet Independent State of Croatia was proclaimed on 10 April. Later that day, Horthy issued a directive to the Hungarian Army ordering it to intervene in Yugoslavia to safeguard the Hungarian minority. The Hungarian government used the pretext that Yugoslavia had ceased to exist, and therefore make the claim that Hungary was not invading it — and on that basis the Hungarian Army crossed the frontier on 11 April. On 13 April, the 1st and 2nd Hungarian Motorized Brigades occupied Novi Sad, then pushed south across the Danube into Syrmia capturing the Croatian towns of Vinkovci and Vukovar on 18 April. These brigades then drove southeast to capture the Serbian town of Valjevo a day later. Other Hungarian forces occupied the regions of Prekmurje and Međimurje. The British considered that Bárdossy's claim was a ludicrous attempt to justify the Hungarian invasion of Yugoslavia, with Eden stating that it would remain an "everlasting shame upon the reputation of Hungary" that she had attacked Yugoslavia a few months after concluding a pact of friendship with her. Even so, Churchill did not declare war on Hungary for some months, despite Eden and Stalin urging him to do so. The Hungarian attack on Yugoslavia has been described by the Hungarian historians Miklós Incze and György Ránki as "the most shameful act of wartime Hungarian policy".