As the election had taken place in his absence, Ottokar did not acknowledge Rudolph as King.
Rudolph himself had promised to regain the "alienated" territories which had to be conferred by the Imperial power with consent of the Prince-electors.
He claimed the Austrian and Carinthian territories for the Empire and summoned Ottokar to the 1275 Reichstag at Würzburg.
By not appearing before the Diet, Ottokar set the events of his demise in motion.
He was placed under the Imperial ban and had all his territorial rights revoked, including even his Bohemian inheritance.

Meanwhile, Rudolph was gathering allies and preparing for battle.
He achieved two of these alliances through the classic Habsburg style – marriage.
First, he married his son Albert to Elisabeth of Gorizia-Tyrol.
In return, her father Count Meinhard II of Gorizia-Tyrol received the Duchy of Carinthia as a fief.
Second, he established an — unstable — alliance with Duke Henry I of Lower Bavaria by offering Rudolph's daughter Katharina as wife for the Duke's son, Otto, in addition to the region of present-day Upper Austria as a pledge for her dowry.
He also concluded an alliance with King Ladislaus IV of Hungary, who intended to settle old scores with Ottokar.

Rudolph, so strengthened, besieged Ottokar at the Austrian capital Vienna in 1276.
Ottokar was forced to surrender and to renounce all his acquisitions, receiving only Bohemia and Moravia as a fief from King Rudolph.
Heavily deprived by this, he was determined to regain his territories and contracted an alliance with the Ascanian Margraves of Brandenburg and the Polish princes.
In 1278 he campaigned against Austria, supported by Duke Henry I of Lower Bavaria, who had switched sides.
Ottokar first laid siege to the towns of Drosendorf and Laa an der Thaya near the Austrian border, while Rudolph decided to leave Vienna and to face the Bohemian army in an open pitched battle in the Morava basin north of the capital, where the Cuman cavalry of King Ladislaus could easily join his forces.
As the election had taken place in his absence, Ottokar did not acknowledge Rudolph as King. Rudolph himself had promised to regain the "alienated" territories which had to be conferred by the Imperial power with consent of the Prince-electors. He claimed the Austrian and Carinthian territories for the Empire and summoned Ottokar to the 1275 Reichstag at Würzburg. By not appearing before the Diet, Ottokar set the events of his demise in motion. He was placed under the Imperial ban and had all his territorial rights revoked, including even his Bohemian inheritance.
Meanwhile, Rudolph was gathering allies and preparing for battle. He achieved two of these alliances through the classic Habsburg style – marriage. First, he married his son Albert to Elisabeth of Gorizia-Tyrol. In return, her father Count Meinhard II of Gorizia-Tyrol received the Duchy of Carinthia as a fief. Second, he established an — unstable — alliance with Duke Henry I of Lower Bavaria by offering Rudolph's daughter Katharina as wife for the Duke's son, Otto, in addition to the region of present-day Upper Austria as a pledge for her dowry. He also concluded an alliance with King Ladislaus IV of Hungary, who intended to settle old scores with Ottokar.
Rudolph, so strengthened, besieged Ottokar at the Austrian capital Vienna in 1276. Ottokar was forced to surrender and to renounce all his acquisitions, receiving only Bohemia and Moravia as a fief from King Rudolph. Heavily deprived by this, he was determined to regain his territories and contracted an alliance with the Ascanian Margraves of Brandenburg and the Polish princes. In 1278 he campaigned against Austria, supported by Duke Henry I of Lower Bavaria, who had switched sides. Ottokar first laid siege to the towns of Drosendorf and Laa an der Thaya near the Austrian border, while Rudolph decided to leave Vienna and to face the Bohemian army in an open pitched battle in the Morava basin north of the capital, where the Cuman cavalry of King Ladislaus could easily join his forces.
Battle on the Marchfeld