Magyar population. The Austrian troops retreated to Austria shortly thereafter to gain more western aid. The Hungarians now stood alone in the defense of their country. The 1241 Mongol invasion first affected Moldavia and Wallachia (situated east and south of the Carpathians). Tens of thousands of Wallachians and Moldavians lost their lives defending their territories from the Golden Horde. Crops and goods plundered from Wallachian settlements seem to have been a primary supply source for the Golden Horde. The invaders killed up to half of the population and burned down most of their settlements, thus destroying much of the cultural and economic records from that period. Neither Wallachians nor the army of Hungary offered much resistance against the Mongols. The swiftness of the invasion took many by surprise and forced them to retreat and hide in forests and the enclosed valleys of the Carpathians. In the end, however, the main target of the invasion was the Kingdom of Hungary. The Hungarian army arrived and encamped at the Sajó River on April 10, 1241, without having been directly challenged by the Mongols. The Mongols, having largely concealed their positions, began their attack the next night; after heavier-than-expected losses inflicted by Hungarian crossbowmen, the Mongols adjusted their strategy and routed the Hungarian forces rapidly. A major Hungarian loss was imminent, and the Mongols intentionally left a gap in their formation to permit the wavering Hungarian forces to flee and spread out in doing so, leaving them unable to effectively resist the Mongols as they picked off the retreating Hungarian remnants. While the king escaped with the help of his bodyguard, the remaining Hungarian army was killed by the Mongols or drowned in the river as they attempted escape. Following their decisive victory, the Mongols now systematically occupied the Great Hungarian Plains, the slopes of the northern Carpathian Mountains, and Transylvania. Where they found local resistance, they killed the population. Where the locale offered no resistance, they forced the men into servitude in the Mongol army. Still, tens of thousands avoided Mongol domination by taking refuge behind the walls of the few existing fortresses or by hiding in the forests or large marshes along the rivers. The Mongols, instead of leaving the defenseless and helpless people and continuing their campaign through Pannonia to Western Europe, spent time securing and pacifying the occupied territories. On Christmas day 1241, the costly siege of Esztergom destroyed