"One cannot wage war under present conditions without the support of public opinion, which is tremendously molded by the press and other forms of propaganda"

This quote by Douglas MacArthur suggests that in order to wage war successfully, public opinion must be taken into account. This is because popular opinion is heavily influenced by the press and other types of propaganda. Simply put, if the press and other kinds of propaganda are not in favor of a war, then popular opinion will be against it, making it tough to wage war. For that reason, in order for a war to be successful, it is important to make sure that popular opinion favors it. This can be done by utilizing the press and other forms of propaganda to form popular opinion in a positive way.