Why did Duryodhana attack Virat’s kingdom?

Why did Duryodhana attack Virat’s kingdom?

Why did Duryodhana attack Virat’s kingdom?

The Pandavas were spending their last year of exile, the Agyaathvaas, at Matsya, where King Virat ruled. His commander was a Suta named Keechaka. He was the queen Sudeshana’s brother. He was so powerful that enemies trembled when he appeared on the battlefield. No one dared attack Matsya while Keechaka commanded the forces. Virat himself was quite afraid of Keechaka and he did not dare say anything against him. 
But Keechaka was killed by Bheema for troubling Draupadi. Spies sent by Duryodhana to find out where the Pandavas are hiding come back to him and tell him that they have no clue where the brothers are. But they also tell him that Keechaka is dead. 
Duryodhana and Karna plan to send better spies to find the Pandavas. But the Kauravas are also keen on strengthening themselves for war now. They need wealth and soldiers and allies. Matysa happens to be a very rich kingdom, thanks to Keechaka’s many exploits until now. It also has a lot of cattle, which is a great wealth for any kingdom plus it is very fertile land. 
Susharma, the Trigartha king, wants revenge for many defeats at Keechaka’s hands. He wants to ally with the Kauravas to attack Matsya. Duryodhana agrees and the plan is made that Susharma will attack first with his army, drawing out Virat and his army. The next day the Kauravas will attack and capture the cattle wealth. 
Everything goes well until Virat gets captured and Bheema takes charge to wallop Susharma. At sunrise the next day, the Kauravas, unaware of Susharma’s fate, attack Matsya, thinking they have an easy job. And then they come face to face with Arjuna.