Duke Ryan was very ambitious and power-hungry, and didn't bear when his authority was contested. He was dissatisfied when Prince Roland was appointed as Border Town's lord but tolerated him due to his origins and confidence in incompetence. Even in front of benefits following by Border Town's development Duke Ryan refused to support it simply because this would hinder his power.
Duke Ryan sent an ambassador to inspect ores prepared for transportation. When Petrov returned and told Roland's decision to directly trade with Willow Town as well as his opinion on this matter, he declared that Western Region was his territory and no one is allowed to disobey him, even a prince.
Osmond was dissatisfied with Earl Elk's unauthorised conspiracy, especially when it failed. He planned to coax Roland after winter, but Timothy's order gave him legitimate right to remove prince from Border Town.
In Longsong Stronghold cold reception shown to Cornelius by Prince Roland as well as his words were widely discussed among nobles. Osmond ordered great nobles to gather forces of around a thousand and five hundred men to attack Border Town.
Osmond's spies informed him about weakened strength of North and the battle between Timothy and Garcia in Eagle City which resulted in the city's burning and heavy losses for both parties. That's why after taking full control over Western Region he planned to conquer Northern Region and establish own kingdom which would be the size of Kingdom of Everwinter. He led Stronghold Alliance forces to quickly supress Roland's resistance and send him back to the King's City, however he lost the battle, was ambushed and killed.
His head was brought by the First Army to Longsong Stronghold to demoralize the enemy and prove that they are victorious.
He saw Roland as an eyesore and wished to be rid of him as soon as possible.