Joshua 11:20 For it was of the LORD to harden their hearts, that they should come against Israel in battle, that he might destroy them utterly, and that they might have no favour, but that he might destroy them, as the LORD commanded Moses.
God had promised Israel this land. He harden their hearts so that they would have to be destroyed.
It is wise to remember that these people knew the truth. They knew who God was. They had known His men, Abraham, Isaac, Jacob, and others. They had heard His stories. They could have tried to make peace earlier like the Gibeonites but they chose not to do so.
Remember that they were choosing their gods and their false religion over the true God of Heaven.
It is easy to see this as God choosing not to save them rather than their destruction being a result of their rebellion against God. They chose not to believe. They chose to continue to serve false gods. They chose their own hardening. They chose their own destruction.
You choose. You can blame things on God but you know the truth. You can repent and seek Him or you can choose to rebel and do what you want to do with your life. If you choose to follow your own paths then you are choosing to hate God and all that He stands for!