What is the theme of The Rangers Apprentice?

We think the theme of the book is remaining loyal and willing to do anything in order to protect your country. For example even though Will knows he might be captured or killed he still decides to destroy the bridge in order to save his country from an invasion that could have put his entire country under slavery or even worse resulted in death for his country's entire population. In the end Will was captured by the Skandians, but he remained loyal to his country.