11th C horses.

[The Wizard]

Eisenhower, IIRC. And indeed, this bears true for modern warfare. But much more so than ancient warfare. Without effective means to blockade large regions and bring nations to their needs without a single battle, tactics enjoyed a position of greater appreciation before the late 19th century. Nowadays, generals busy themselves with strategy, and lower rank officers with tactics. This was different before (although it is not clear anymore when tactics end and strategy begins these days).

An army like that of the Mongols had little to no supply line. This, in turn, gave them their immense mobility and therefore ability to take the initiative at all times.