"We need to create the world Luis Santiago would have wanted, for his children, my children and posterity."
"We will begin by focusing on the needs of our own people to sustain them through this difficult time and prepare them for the tasks ahead."
- – EA President William Morgan Clark, January 1, 2259
William Morgan Clark was the Vice President of EA President Luis Santiago and later became the President of the Earth Alliance. While in office, he instituted a reign of terror over the Earth Alliance and became a dictator. He ruled Earth with an iron fist for nearly three years, before finally being overthrown by Captain John Sheridan.
Early presidencyClark became president when Earthforce One, carrying President Luis Santiago, was destroyed at the Io Transfer point on January 1, 2259. He was complicit with the assassination, in order to take office. He believed Earth to be in danger of being overrun by extraterrestrial races, and so the Nightwatch, a fascist, paramilitary organization, was created to find out people suspected to be alien infiltrators or sympathizers.
Earthforce's Chairman of the Joint Chiefs of Staff, General William Hague, suspected that Clark was involved in the assassination, and began a low-level counter-conspiracy that included Captain John Sheridan. In 2260, John Sheridan and General Hague found solid evidence that Clark had arranged the assassination of Santiago. Hague managed to get the evidence introduced in the Senate, which caused an uproar.
At about the same time, it was revealed that Clark's forces - along with the Psi Corps - had found a Shadow vessel buried on Ganymede. Clark was having the ship studied in order to learn its secrets. John Sheridan took the White Star back to Ganymede, and destroyed the vessel. Clark soon issued a decree of martial law using the Ganymede incident as an excuse.
When martial law was declared, Hague began armed resistance against Clark's government. Hague was soon killed in a firefight between his ship, the EAS Alexander and the heavy-cruiser EAS Clarkstown. Meanwhile, Mars rejected martial law, and Clark responded by bombing Mars.
Clark dissolved the Senate, and nationalized the media outlets. In response, Proxima III and Orion VII broke away from the Earth Alliance, setting themselves up as independent states. Babylon 5 soon followed these two colonies by breaking away , after Clark attempted and failed to seize the station and put it under command of the Nightwatch. Clark quickly turned the Earth Alliance into a dictatorship, going as far as sending the military to seize media networks, including ISN, which was remade into a propaganda machine. Considering Sheridan to be a threat, Clark targeted Babylon 5 and Sheridan specifically with a blockade and a propaganda war to sway public opinion in favor of his police state. 
In the fall of 2261, Clark put a policy in place of killing refugees trying to leave the colonies that he was taking military action against. When Sheridan learned that in one case 10,000 innocent civilians were killed by an Earth Alliance vessel, he realized that the time had come to remove Clark. Sheridan after the Shadow War had built a powerful alliance of races and held command of the Whitestar Fleet, giving him the military muscle to fight Earth directly. Sheridan's forces began a systematic campaign against Clark's forces, including a televised message of their own dubbed the "Voice of the Resistance". Large numbers of Earth Force personnel defected, and Sheridan scored his first major victory against Clark by defeating his forces blockading Proxima III. Sheridan himself was eventually captured by his former chief of security Michael Garibaldi and tortured, but was rescued and returned to the fleet soon afterward, which by this time had grown to include a large number of Earth Force ships fighting alongside him.
Clark decided to trap Sheridan's forces with advanced model destroyers that had been fitted with Shadow technology. When Sheridan's second in command, Commander Susan Ivanova, learned of this, she engaged the destroyers with the White Star ships, leaving the rest of the Earthforce vessels behind. Captain James of the EAS Agamemnon opposed Ivanova's decision, but soon realized that Clark would have his destroyers target the Earth ships rather than the White Stars. While Ivanova managed to destroy all the vessels, her White Star was severely damaged by a collision with debris from one of the destroyed vessels she was injured and left in a near-death state.
Suicide and legacyEventually, Sheridan took the fleet directly to Earth, and sent a message saying that they had come home to fight against Clark's tyranny. Realizing that he would soon be captured, Clark committed suicide with a PPG. In one last vindictive act, he turned the planetary defense grid back on to Earth under a "scorched earth" policy. Sheridan and his forces, however, were able to destroy the defense platforms before they fired; Sheridan was prepared to ram the final platform (targeting North America's eastern seaboard) with his badly damaged ship, but the EAS Apollo (previously fighting against Sheridan) appeared to destroy the platform and save Sheridan's life..
After Clark's suicide, Susanna Luchenko of the Russian Consortium was named President. President Luchenko announced that the justice department would prosecute those who had committed crimes during Clark's reign of terror and offered amnesty to those who had followed Sheridan. Sheridan would resign in the aftermath of the civil war.
Though Clark's dictatorial regime ended, some of his collaborators survived the fall of the dictatorship and the subsequent Senate investigations, some even retaining positions within EarthGov, as was the case with Clark's speech writer turned political commentator Henry Ellis and Mr. Welles of the Nightwatch Division.