I'm not American, but I am a historian. I view the entire Pacific theatre as something which could have been avoided, but American foreign policy choices and colonial ambitions forced the issue. America did not, however, necessarily want war with Japan. A land invasion of Japan would have resulted in cataclysmic population collapse, if not outright ethnic cleansing as a consequence of existing Japanese culture and supply constraints. Across the Pacific theatre, Japan operated under what was close to a "no retreat" doctrine; strategic repositioning could be justified, but ceding territory to mitigate losses was not. It was expected, and required often, that soldiers and civilians both would give their lives for the Emperor. To be clear, this is not an indictment against Japan's honour, as its men fought bravely and legitimately believed that they were fighting an implacable, possibly genocidal threat. The Americans, after all, did not have perfectly friendly relations with Japan for the prior century. This attitude, and the belief that terrible harms would come upon Japanese women and children, resulted in horrific and avoidable tragedies. There are many stories from Marine veterans of civilians killing themselves when they successfully occupied an island or village. A few hundred, maybe a thousand here and there, but these events were significant enough they made it to American high command and had US troops seriously questioning what they were doing. And it was for this reason that a mass shock-and-awe decisive strike was planned, to force the unconditional surrender. The American people still wanted revenge and a conditional surrender would not have been that, and, American command wanted to mitigate the damage to civilians because they knew full-well what would happen in the case of a ground invasion. The final point to take note of is, in the months leading up to the bombing of Hiroshima and Nagasaki, the Imperial Japanese Army had started training civilian men and women to fight, using everything from farm tools to sharpened bamboo spears. Whether or not this was out of genuine fear or not is irrelevant; it trains the populace to expect certain things and behave in certain ways. So, in the case of a ground invasion without the use of nuclear weapons: A wave of bombers strikes Japanese airfields first, destroying most of them essentially overnight. They also target and destroy any military bases they can find, as the US planes can simply fly higher than the Japanese interceptors. This goes on for two weeks, with a final ultimatum issued: Surrender or the mainland will be invaded. The Japanese generals refuse. America lands its troops across the Eastern coasts, moving inland rapidly. Warships bombard cities and fortifications, while overhead planes firebomb everything. Even trying to mitigate damages and warning civilians to evacuate, many stay behind to fight and are slaughtered by the thousands. American troops arrive to razed cities with few scattered defenders, most too poorly equipped to present a real threat. Word gets out to the government of Japan, who declares that this is an existential war and that everyone must fight. The Soviets now, having finished in Germany, are turning Eastward and are moving to invade Hokkaido as well as Japan's remaining territories in continental Asia. Already stretched thin defending against America, the Soviets quickly move in and take over. Thousands of Japanese women, having colonized these provinces when they were conquered, are raped. They later go on to form a distinct local ethnicity of mixed Russo-Japanese people, with much of those continental territories and Hokkaido permanently changed, demographically. Back on the Mainland, Japan's industrial centres are gone. Instead of nuking them, Hiroshima and Nagasaki are firebombed and the cities do not survive. The devastation and casualty numbers are similar, albeit drawn out over several weeks of sustained bombardment. Due to interruptions in food supplies, millions of urban civilians starve. Many lose faith in the Japanese government and decide to seek refuge in American-built concentration camps where they at least receive food and shelter. These camps are not safe either, however, as while Americans violently punish any rapists found amongst their number, many rapes do still occur. Children trying to protect their mothers are viciously beaten, and this reaches the American mainland as a series of scandals. Every mile of land secured by American forces comes with at least 50% casualty rates among the locals, often by their own hands, sometimes when they attack American troops. Traps severely damage American troops' morale, but aren't common issues as they push towards Japan's capital. Upon reaching it, the Emperor is quickly found, surrounded, imprisoned and forced to surrender. A press statement is issued, broadcast to every city, every internment camp, every newspaper, etc., mirroring the one we saw in real life. Accompanying it, however, is a declaration that Japan is now an American colony. Administratively, Japan loses its autonomy. It is given a constitution much more restrictive than the one in real life, however, much of the worst consequences are still avoided for the same reasons as in real life. The major differences are mass depopulation, permanent American bases across the entirety of Japan, and the complete loss of its Northern isles. Hokkaido becomes a Soviet province, completely alien in culture and language from the rest of Japan, forming a North/South Japan not unlike Korea. The entire island is demographically changed, with a large influx of American men taking Japanese women as wives; primarily due to so many of Japan's men being wiped out during the war. Modern parallels to this is Ukrainian women. Japanese itself becomes a secondary, local ethnic language whilst the primary language is English. This is, primarily, for ease of communication between the provisional government of Japan and America. In this alternate timeline, Communism is much more powerful of a force in Japan as well, thanks to both Soviet and CIA subversion within the country. Its identity already damaged heavily from the war, and demographic changes, it's possible that 'South Japan' ends up seeking unification with 'North Japan', with a constant and persistent risk of violent revolution. That's a bit harder to predict, however. All in all, while I absolutely loathe the loss of life from using nuclear weapons, I do truly believe it was the lesser of two evils. The alternative sees Japan demographically ruined and its culture annihilated, while losing territory to the Soviets who continue to push their weight around militarily. Without the fear of nuclear exchange, there's no reason for the soviets to ever stop in their expansionism besides domestic tensions and so the second half of the 20th century would have been much bloodier all around. A terrible case where it was necessary to sacrifice a few, for the sake of the many. Both in Japan, and around the world.