Short answers, pulled from the story.
The 36-day assault resulted in more than 26,000 American casualties, including 6,800 dead. Of the approximately 21,000 Japanese soldiers on the island at the start of the battle, only 216 were taken prisoner. Iwo Jima was the only Pacific War amphibious battle where total American casualties exceeded those of the Japanese.
Joe Rosenthal of the Associated Press photographed the second flag-raising on Mount Suribachi on the 23rd of February 1945. The photograph became the only image to win the Pulitzer Prize for Photography in the same year it was published, and is regarded as one of the most reproduced photographs ever made.
Kuribayashi rejected the traditional Japanese tactic of contesting landings at the beach and instead built defenses in depth, relying on 18 km of tunnels, underground bunkers, camouflaged artillery, and mutually supporting fortifications. His strategy allowed positions cleared by Marines to be reoccupied by troops moving underground, and he strictly forbade the mass banzai charges that had failed in previous battles.
Six Navajo code talkers transmitted over 800 error-free messages during the first two days of the landing. They served as forward observers, relaying artillery strike coordinates from the island to command ships and transmitting orders back to shore. Major Howard Connor, the 5th Marine Division signal officer, stated that without the Navajos, the Marines would never have taken Iwo Jima.
The strategic value of Iwo Jima was disputed even during the war. Retired Chief of Naval Operations William V. Pratt declared in April 1945 that the island was useless to both the Army and the Navy. Only ten P-51 Mustang bomber escort missions were flown from the island before the bombing campaign shifted to nighttime raids, and a later Air Force study found the contribution of the fighter command based there to be superfluous.
More than 3,000 Japanese troops continued to resist inside cave systems after the island was declared secure. The U.S. Army's 147th Infantry Regiment spent three months hunting them down. Two holdouts from Lieutenant Toshihiko Ohno's unit evaded capture for four years, finally surrendering on the 6th of January 1949.