Why did Isengard's army attack Helm's Deep?

In this video, we look at why Saruman's army from Isengard attacked the powerful fortress of Helm's Deep instead of invading weaker and less well-defended parts of Rohan. Thanks to my patrons - Wags, Skjoldmø, bearandwolf, Will Harrison, Slowbro96, Vasco Sa Pinto, Gavin, Javi Iñesta ,Brn, JIV, Fipse, W Sean Mason, boi sophies, Stonetruck, ThunderStryken, Hallimar Rathlorn, Habimana, Ben Jeffrey, Harry Evett, Mojtaba Ro, Moe L, Paul Leone, Barbossa, mncb1o, Carrot Ifson, Andrew Welch and Catherine Berry Patreon -   / darthgandalf