So Teddy Roosevelt above everything else believed in personal strength, and the need to devote oneself to causes worthy of it.

First we should point out he more than anything, indeed in some ways more than president, he was a Navy Man in his heart. While at Harvard in the 1870's he published the work that for most of a century was THE standard work on the US Navy int he War of 1812. He was absolutely learned and astute in Naval works and a major supporter of the great American theorist Alfred Thayer Mahan.

But his family situation, class expectations, and his at times sickly nature precluded service at sea. But he never lost that connection as he entered politics after hi stint as a rancher out West. His campaign work and time as the Ney York City Police Commissioner helped raise his profile in the GOP.

Also important was that he was a member of that grand Old Boys Network that encompassed the WASPs of the North East and was cemented in the Ivy league Colleges.

One of TR's close allies and good friends then was the influential Congressman Henry Cabot Lodge. Lodge once McKinley was in need of a new Asst SECNAV, Lodge supported his old friend who he knew would relish the opportunity for the post. Roosevelt worked hard and was essentially running the Navy, Secretary long was relatively hands off and uninterested, thus it was Roosevelt doing things like sending the warning messages and placing Dewey's Asiatic Squadron where it could attack Manila.

But when the fighting started Roosevelt thought he could not sit behind a desk that his honor, and future prospects demanded he test himself against the Spaniards in Cuba, so he resigned as Asst SECNAV.

This quote should give you an idea about what came across as his underlying motivations and why he wasn't content to sit in DC.

Brands calls Roosevelt "the last romantic", arguing that his romantic concept of life emerged from his belief that "physical bravery was the highest virtue and war the ultimate test of bravery".

Henry Adams a descendent of the Presidents and great Historian said of him:

Roosevelt, more than any other man... showed the singular primitive quality that belongs to ultimate matter—the quality that medieval theology assigned to God—he was pure act

The Spanish American war was also essentially the last one fought before the modern National guard system was organized. Instead it was fought very much as the Civil War had, with individual states and persons of influence organizing units, with the intent of then being granted commissions in them.

TR knew he wasn't a true military leader yet, so he was able to grab his friend, and the doctor of the President Colonel Leonard Wood, who had been a career soldier out West, to command the Rough Riders. He then filled the ranks with men he had known from Harvard and men he recruited through his old ranching connections, and got himself placed as the 2nd in Command. And off the went to Cuba, and what he termed his 'Crowded hour" at San Juan.

The actual process of what he did, serving as an officer in the Volunteers, and having high rank from social power, is not that rare for the time. What made it stand out was simply his success at public relations, and the unprecedented amount of news coverage the war had along with Roosevelt's charm, macho man attitude, and drive to scale the political ladder as he went.

But because he refused to give up and sit by the side when he thought other men were not up to the task it led to his somewhat ridiculed attempts to lead in WW1, when he was well past his prime and would most likely have been out of his depth. He just didn't have it in him to sit at home when men were fighting, especially when it was his sons.

And excellent work on the interlocking personalities involved at the time is: The War Lovers: Roosevelt, Lodge, Hearst, and the Rush to Empire, 1898 by Evan Thomas.