How did the electric telegraph change military command during the 1800s?

The electric telegraph fundamentally transformed 19th-century military command by replacing slow, mounted messengers with rapid, wire-based communication. This shift allowed commanders to exercise active control over armies separated by vast distances, often spanning miles or tens of miles.1

Key impacts on military command included:

• Centralization of Command: Commanders and their staffs increasingly moved from the battlefield to rear headquarters, shifting their focus from direct observation to analyzing reports and maps.1
• Deliberate Decision-Making: The traditional coup d’oeil—a commander making immediate decisions based on a battlefield glance—was replaced by the "estimate of the situation," a process characterized by cooler, more detached deliberation.1
• Operational Reach: During the 1866 Prussian campaign, field telegraphs enabled commanders like Helmuth von Moltke to effectively manage distant armies.2
• Logistical Evolution: Armies began organizing mobile telegraph trains, such as those used by the Union army during the American Civil War, to maintain connectivity as forces moved.2

While the telegraph significantly increased the speed of information, its reliance on fixed, wired systems eventually favored defensive operations by tethering commanders to immobile headquarters.1