I'll try

Before the Meiji restoration, Japan was largely self-sufficient with its rich soils and it was caught in numerous wars between its constituent clans. After the fact, Japan would centralize its power and create a strong military based on the western model (numerous mission from the British, the French and the Americans). Seeing that pretty much the entirety of Asia was under Western Control and witnessing what happened to China (The unequal treaties after the Opium Wars), it had to get itself a Navy and an Army.

The Army and different factions in the Navy had very different ideas of how to defend Japan, a problem which will persist up until the end of the Second World War. The Army advocated for its own primacy stating that ground troops would be needed to defend the home islands. The Navy was split, some thought offensive was the best form of defense while others preferred to relegate the Navy to a coastal defense role. Japan had but very limited interaction with the seas, a lack of continental enemy (minus the mongols) and was isolationist for a long time. The Navy had to find for itself a raison d'être.

Nevertheless, with the both services expanding and the country expanding at ASTOUNDING RATE, it was clear that the home islands wouldn't be able to supply them with the needed raw materials. It is in itself a national security issue. Fast-forward, Japan goes to war against China in 1895 and Russia in 1905 over national security concerns. Emboldened by those two victories and their gains in WW1, the expansionist clique gained influence. Conversely, up to the 1930s, the pacifist clique within the armed forces were still going strong which signed the naval treaties of 1922 and 1930.

For a while, the country had known a period, the Taisho-Democracy era. Unfortunately, failure to obtain what they wanted from the Naval Treaties and the Great depression exacerbated the feelings of the Right-Wing elements. The civil government which had no control over the military saw the latter become more and more adventurous. From 1930s onward, a big emphasis was placed on emperor worship and bushido. By then, the Japanese already had serious influence over various parts of China, especially Manchuria. With the economic crisis, over spilling population, the amount already invested in the area as well as the presence of a large army, Manchuria was attractive for its land and resources. China was still fragmented and politically weak and a conquest would be relatively easy.

From the beginning, Japan had always had problem with fuel whether it be coal or oil. After leaving the League of Nation, not renewing the pact in 1936, joining the Axis in 1940 and sending troops to indochina, Japan was being more and more isolated. It would lack the metals and the fuel so critical to their status as a second or even first rate power, an obsession of theirs. The doctrine of the imperial armed forces switched from Honshin (Russia) to Nanshin (south east asia), but up to the end officers such as Yonai, Yamamoto and Inoue believed that a war could be averted. This is of course subject to many debate. Indeed the Army suddenly started preaching for the Nanshin-ron to gain material that would help them finish the China war and the Navy wanted to obtain fuel and naval bases for their fleet.With the hypothetical enemy going from Russia to Germany to the US to the US, China, GB, France, the Dutch and even possibly the USSR, you can see how emboldened they had become. And since as early as the end of the Russo-Japanese war, many expected a war in the Pacific against the US with some outright wishing for it. It wasn't exactly a sudden thing.

With the Imperial Policy finally set to an invasion of South East Asia, the issue would be to either invade the Netherlands's east Indies first or the Philippines. The Navy advocated a swift destruction of the American Asiatic Fleet and the occupation of the Philippines before the US could reinforce it. Indeed, it stood between the East Indies and the home island and was a threat to Japanese routes. Luftwaffe performance in the Battle of Norway seemed to have proven to the IJN of the usefulness of land-based aircraft in naval battle and wanted to use Philippines-based airbase to invade the Netherlands east indies (indeed, Taiwan+Indochina were a bit too far for that). The Army, scared that the British would reinforce the Netherlands east indies and Malaya advocated for the opposite because of their hunger for resources. The compromise was a coordinated invasion of both and the maneuver was largely successful as the Japanese had overestimate Allied strength in the area and had prepared consequently. The IJN by attacking the Philippines initially wanted to do so to also draw the US Pacific Fleet to the western Pacific for a the traditional Mahanian Decisive Battle on which all their planning and production depended on. Very early on, some naval officers had, in hindsight, correctly cast some doubt over the strategy. With those doubts and careful studies of the British attack on the Italian Base at Taranto and the naval battle of Mers El-kebir, advocates of air power would produce what would become the IJN Directive No.1 in November 1941: The attack on Pearl Harbor. This attack would change the course of history and the popular conception that it was done so to win some time for the invasion of SEA is correct.

TLDR: reasons are essentially obsession in being a first-rate nation; lack of resources mostly metals, oil and rubber; emboldened ultranationalist faction in the 1930s; apparent success of the blitzkrieg in Europe; Operation Barbarossa keeping the Russians busy. Racism was a factor. Paradoxically, the Japanese still saw the Chinese as somewhat of a big brother that they absolutely had to surpass. I feel like they saw them as a formerly amazing brother that went to shit. They then went on the hold them in contempt and see them as backwards.

Sources: Dower - Embracing defeat

Evans - Kaigun

Toland - The Rising sun

Morison - The Two-Ocean war