Axis leaders making poor decisions during World War II is nothing strange, but Pearl Harbor seems to be such a comically bad decision, one that makes absolutely no sense to me. To me it seems like they attacked one of the most powerful nations in the world at the time and guaranteed the addition of another enemy into the war. Is this just the value of hindsight or is there anything I'm missing that makes this decision make sense at the time?
No, it wasn't a great idea. Plenty more can be said, but you might want to check out these older answers:
https://www.reddit.com/r/AskHistorians/comments/80xu8w/did_the_japanese_seriously_consider_invading/
One major issue here is seeing the Pearl Harbor attack in isolation, which is a very American "homeland" focused view.
The Pearl Harbor attack was just one component of a larger campaign of attacks across Southeast Asia and the Pacific targeting American and British held territories and forces. The Pearl Harbor attack was designed primarily as a means to forestall a rapid response to those attacks which could jeopardize their success. They simultaneously attacked British held Malaya, Hong Kong, and Singapore, the Dutch East Indies (Indonesia), along with the American held Philippine islands, Guam, and Wake island. Within a matter of days Japanese forces conquered Guam and Wake Island, while Hong Kong fell before the end of the month. Singapore and Malaya fell within 2 months, the Dutch East Indies were conquered by March, and the Philippines by May.
The Japanese did not merely declare war on the US on December 7th but also all of the major nations of the British commonwealth at the time (Great Britain, Canada, Australia, New Zealand, and South Africa).
Their intent was to consolidate a hold on a defensible set of territories in the vicinity of the Japanese home islands and their important territorial possessions. And, critically, to acquire access to natural resources like petroleum, rubber, and bauxite necessary to maintain Japan's ability to make war which were not available on the home islands.
The Japanese were expecting hostilities to escalate with the anglospheric powers, especially as the war in Europe had escalated and they had become cozy with the Nazis and Fascists through the Tripartite Pact signed a year before. Was it a good decision for them to attack several major world powers and sneak attack the world's largest industrial and naval power? Obviously not, as it did not work out very well for them. But the question is really what other options they had available. If you start from the assumption that the Japanese empire was already wedded to the principle of maintaining an empire in East Asia. You add to that the loss of the option of being able to engage with the aglospheric powers in a state of indifference to Japanese aggression due to boycotts by American industry and by mid-1941 much harsher measures such as the US government freezing Japanese assets. You add to that entering into an intentionally hostile stance by allying with Nazi Germany and Fascist Italy in 1940. An alliance that Japan entered into after the British commonwealth nations and France had already declared war against Germany, putting them objectively in at least indirect conflict. And by early 1941 with the Lend-Lease program marking America's soft entry into WWII by allowing it to serve as a main supplier of Allied countries Japan had set themselves up to be in opposition to them as well.
In that context conflict was inevitable if Japan was to continue its regional aggression and the only decision was to figure out how to make the most of it. Consolidating territory in Asia was practically a necessity for the reasons I outlined above. If Japan were to come into direct conflict with the US or Great Britain then it would be very bad for them indeed if those powers held Malaya, the Philippines, Guam, Hong Kong, etc. And, indeed, we saw in the end of the War in the Pacific what it meant when the Allies held some of those territories. It made it possible to interdict Japanese shipping and get a stranglehold on the lifeblood that was not only allowing the Japanese military machine to operate but was keeping the Japanese home islands fed and alive. The attacks on American and British et al territories in Asia were an attempt to eliminate that eventuality.
And once you have committed to those invasions then the major question becomes what happens next. In those circumstances you cannot escape entering into a state of war with the US and Great Britain. In that case the thing to fear the most would be the response of the potent American Pacific Fleet. So then, logically, you would seek to neutralize that fleet as best you can in order to give your forces time to make their wins and consolidate their holds on captured territory, which they did.
It was a poor decision but they were virtually locked in to bad outcomes from all of their preceding decisions.
One might imagine a parallel universe where the Japanese Empire did not join into the Axis Powers and instead tried to play a more cautious game of pretending at some sort of "kinder, gentler" conquering of East Asia coupled with some sort of clever peaceful political arrangement with the US. Or, perhaps we could imagine the Japanese engineering some kind of ruse where they could dupe the US into attacking them as a means of initiating conflict, which could potentially have sapped some of the political will for the Pacific War on the American homefront and opened up the possibility for some kind of negotiated settlement to the conflict. But all of that relies on a great number of what-ifs and strong counter-factuals. The reality was that once Japan had set itself as a member of the Axis Powers and once it had committed itself to aggressively conquering much of East and Southeast Asia it was irrevocably headed for conflict with the US and Great Britain et al. And once committed to that conflict there were few moves that could gain Japan even temporary advantage. From Japan's viewpoint the consolidation of territory and neutralization of the Pacific Fleet were the best ways to achieve the greatest advantage, so that's what they did.
And it totally worked. Briefly. There was no way the Japanese could win a war against the US, but that was set in stone in 1940 or 1937, not 1941.
One of the oddities of Pearl Harbor was that two Americans taught the Japanese to do it.
The second was President Theodore Roosevelt, who cheered on the Japanese surprise attack on the Russian Pacific Squadron at the Battle of Port Arthur of 8–9 February 1904. Ten Japanese motor torpedo boats made a surprise night attack inside the port, but the damage was limited by anti-torpedo nets and shore batteries that began to pound the Japanese into beating a hasty retreat.
The first was US Navy Captain Alfred Thayer Mahan (September 27, 1840 – December 1, 1914) was a United States naval officer, historian, and, according to John Keegan "the most important American strategist of the nineteenth century."
His book The Influence of Sea Power Upon History, 1660–1783 (1890) was translated by Kanô Jigorô, the founder of jûdô, and his colleagues at the Kaiji Kyôkai Maritime Affairs Association within months of its publication; eventually many if not most of Mahan's works were translated into Japanese and were very influential upon the development of the Imperial Japanese Navy, where his concepts and histories were taught at all levels of professional development.
Mahan's strategic theory has been shortened from the three volumes essentially to the concentration of a nation's fleet in order to seek out and destroy the enemy fleet in a decisive naval battle. Decisive naval battle in the early days of the 20th century meant large surface combatants, which were limited in the arms treaties Japan adhered to until the final one expired.
Only late in the game did the Japanese get interested in naval aviation - when then Captain Yamamoto Isoroku went to his assignment as the Japanese naval attaché (essentially an openly declared intelligence collector) for the Japanese embassy in Washington, D.C., from 1926 to 1927, his predecessor advised him to pay attention to what the Americans were doing with naval aviation. His predecessor went back to Japan and become the brains behind Japan's naval aviation effort.
Mahan's 'decisive naval battle' in part led the Japanese to focus on large surface combatants, the culmination of which was the Yamato class super battleships. One aspect of their strategic planning was the correlation of forces - some Japanese took 1936 as the optimal time to attack the US Navy, when a number of new Japanese capital ships came online and before the production capability of America could be used to overpower Japan.
The focus on surface warfare diverted resources from other assets that probably would have served the Japanese better. The Yamato class superbattleships were hugely expensive, but obsolete before their keels were laid down.
Others have written well on the 'logic' or lack of it, but at some level it was meant to weaken the US Pacific Fleet before the 'decisive battle', no matter how unlikely it looks in retrospect. But Yamamoto himself warned against attacking Pearl Harbor; his time in America convinced him that Japan could never outproduce America if it mobilized its massive resources and industry.