Actually, “shout” sounds good in this context since it’s an turning point in character’s life and in the storyline. Think of the emotions everyone’s experiencing in their first ever battle. Besides, did the king make the right decision to send his army to fight another one? Just ask yourself some questions like that and the answer will definitely be found. If you still want to emphasize his fury you may say “bellowed”, especially if the king’s old. There are some other options that are suitable: “yelled”, “raged”, “rallied” or just “said”. It’s totally up to you what to write but once you choose the right word, stick to that feeling it expresses.