Japan at least in the Pacific theater was driven to circumstance and openly declaring war on the US would be suicide. Japan needed to gain resources in the Pacific and the only threat was the US. It had to attack the majority of the Pacific Fleet while it was docked and not mobilized yet.

Japan at 1941 was in a crisis that would halt it’s army and navy. The US, UK, and Dutch all put an embargo on the Japanese due to their expansion into China and annexation of French Indochina. Fearing their own colonies could be targeted next, they stopped all shipments of resources to Japan. This included iron, steel, aluminum, copper, rubber and most importantly oil. Though the wholesale embargo of oil was not in effect until summer of 1941 as the US avoided banning all oil from Japan. Japan relied heavily on oil from the US, around 80% of their oil came from the US. This was devastating to say the least and Japan could not survive in this condition. These powers gave Japan an ultimatum of backing out of China and French Indochina and return to the borders pre-invasion of Manchuria and dissolve the Tripartite Pact.

Japan now faced a dilemma: obey the West’s demands or keep on expanding. Both would lead to ruin and the destruction of Japan. Japan then thought of the only way to save it’s empire: attack the West and seize their resources. If Japan could take the Dutch East Indies and British Malaya they would be set on most of their resource needs including oil. While Japan had set sites on these places before the embargo, Japan knew it couldn’t while the US Pacific Fleet was still active. Hence why they attacked Pearl Harbor and why they attacked with no declaration of war. Japan had one chance to wipe out the US Fleet and then establish control in the Pacific. If it gave the US too much of a warning such as declaration of war, it would blow any chance of Japan winning the war with the US. Even though it had surprised the US, it did not put them at a major disadvantage as the Japanese wanted The aircraft carriers and subs were untouched during the attack alongside the entire oil reserve for the Pacific Fleet.

If I had to say why Japan attacks without declaring war on another country is speed. Japan is usually facing larger and stronger opponents in war. They can’t bear a long attritional war like Russia or the US can. It needs to win it’s war quick with decisive battles that end the conflict in it’s favor. So if the opportunity arises to strike their opponent while they are vulnerable, they take it.

Source:

Toland, John Willard. The Rising Sun the Decline and Fall of the Japanese Empire, 1936-1945. Modern Library, 2003.

First let me address the samurai tactics. There is some truth to what you say, that these surprised attacks were influence by a samurai understanding of war, but only indirectly and is a little questionable. Generally, Japan adopted a limited and quick war strategy from Germany. The French based strategy started to win out in favor of Prussian strategy. Certainly, the samurai loved Clausewitz, and especially his ideas on the "intangibles of war." So they may have been more fond of the German way of war culturally, but it was also a practical strategy for them., the Meiji reformers were samurai, like that great scene in "The Last Samurai" where he says "He is samurai" to the mustached Japanese officer. They hired Major Jakob Meckel from Prussia to train their first professional officer corps. Anyways, Japan felt as if its position was similar to that of Germany's- a nation with few resources with potential enemy's surrounding it. The book by S.C. Paine that I will cite below is primarily a critique on this security strategy. Japan went with a limited quick war strategy adapted from Germany because it had few resources, and also maybe because samurai generally really liked Clausewitz and other Prussian military theorists.

Surprise attacks came more out of a necessity for a quick decisive war rather than a military strategy or policy in and of itself. In both the Russo-Japanese war and Pacific War, Japan faced an enemy with far greater population and economic production, that happened to have small militaries far from their economic centers. A decisive blow was key, and what better time to strike that blow than right before you declare war.

Diplomatic impacts of surprise attacks were initially softened by the weste viewing the Aisan states as backwards with racially inferior people. Tsar Nicholas II (the one killed by the Bolsheviks) had regular racist correspondence with Wilhelm over the Japanese. Referred to the Japanese as little mokeys, ect. Western nation really did not hold Japan to the same western standards until after the Russo Japanese war.

1. The First Sino-Japanese war- This was not really started with a surprise. Japan and China had already been dancing around war with each other over Korea. The Tonghak rebellion kicked off and the Korean king asked for forces from China. Realizing this would give China huge influence in Korea, Japan sent troops as well. Japan refused to withdraw its troops and captured the Korean king. The Japanese and Chinese navy eventually exchanged fire, and Japan sunk a British steamer that was ferrying Chinese troops. So it was kind of a surprise, and kind of a surprise between two Asian nations. Also, Japan claimed that it was legal for them to sink Kowshing by maritime law.
2. The Russo-Japanese War- China had agreed in concessions from the FSJW to not lease Lushun (port Arthur) to any other power. They then leased it to Russia because of pressure from Russia. Russia refused to divide up spheres of influences in Manchuria and Korea with Japan. Japan viewed Korea as vital to its survival, and was not willing to give it up. The Tsar would not negotiate for these spheres, and Japan viewed war with Russia as inevitable. Japan knew that Russia had superior resources, superior fleet, and more population, but Japan had distance on their side. The Trans Siberian Railroad was being finished, and Japan sought to win a war before it was completed. Japan viewed a quick war as necessary to victory, and it was. Russia had a larger fleet docked at Port Arthur, and could transport a large army part of the way with the Trans-Siberian RR. They viewed a surprise attack as necessary to cripple Russia's fleet. Japan struck at the ships in harbor with torpedo boats three hours before declaring war. Ultimately, Japan had a great exit strategy as diplomats had already made connections with the US, and planned to broker a favorable peace using the US as an intermediary that they had already got on their side. Russia had also lost its prized Baltic fleet in the Battle of Tsushima. The loss of a western fleet to an Asian power was far more shocking than Japan braking the Hague Conventions. Japan was not held to the same standard as other western powers, often due to a quite frankly racist view of the Japanese. Japan also won a war against Russia, which shocked the west. The world then got embroiled in WWI, and had other things to think about than Japan breaking the Hague
3. The Second-Sino Japanese war- This was again not really a surprise attack. It was much more a slowly escalating war, that is hard to put a date on when it even started. It could have been the Manchurian Incident in 1931. Japanese officers planned a coup to takeover Manchuria. This was done without knowledge from the Japanese civilian government and many in the Japanese high command. It was a Fait Accompli and a surprise attack on Manchuria. It was not a planned attack by the Japanese government or larger military however, and was done to "free" the Manchus and secure the Japanese railroad. This essentially put Japan at complete odds with a China that would not accept a separate Manchuria. While that incident was a surprise but most agree that he Marco-Polo Bridge Incident in 1937 was what kicked off the war, which was a dispute over a missing Japanese soldier. This war was a slow escalation of both sides committing more and more to the fighting, and not an outright war from the very start. Both sides would fight and negotiate, with the fighting getting worse and worse as Japan's demands grew larger and larger, leading to all out war. However, it is important to note that these incidents show a larger problem, Japanese military acting on its own behalf without regard from the civilian government in diplomacy. The conflict in China would eventually bring them at odds with America.
4. Pacific War- Japanese high command were not stupid. They knew that they could not fight a protracted war against the economic power house of US. However, two finance ministers expressed the scope of the danger of attacking America, and one would be assassinated for his comments. Anyways, they had a larger navy, with the largest battleships in the world. America had cut off oil and demanded Japan retreat completely from China, and even Manchuria, giving up more territory than it had before the war. They decided to do a surprise attack to cripple America's fleet in order to have a quick end with oil possessions in the South Pacific. They expected America to roll over and sue for peace instead of engaging in a prolonged war. Operation Ke-Sakusen was an operational success, taking the Americans completely by surprise and crippling their fleet. Japan attacked an hour before declaring war with the US. The Japanese attacks happened within hours of each other, and may not have been possible if the British and Americans had been prepared for it. It was however a colossal disaster for the Japanese strategy by completely turning the American people towards war. America lost its isolationist attitude completely. Japan had no exit strategy. No way in which to negotiate or convince America to stop the war. America could invade Japan, Japan could not do the same to America, and this was a diplomatic disaster that would hound Japan into unconditional surrender.

So yeah, Japan pursued a limited and quick war strategy because of its resource situation. The First and Second Sino-Japanese wars were kind of surprises, but the Russo and Pacific wars were assuredly surprises. In all but the Second Sino-Japanese war, did Japan view their forces as greater than the opposing side's, so a surprise attack was viewed as necessary for success. This was not really a samurai tactic directly, but of course the Meiji reformers were samurai. As far as the diplomatic effects and the perception of it violating the Hague... Well if the 20th century taught us anything it is that international law is "More of a guideline than actual rules." But the surprise attack on Pearl Harbor, and the sneakiness in which the American population viewed the attack, would have dire consequences for the Japanese state.

Japan's Imperial Army: Its Rise and Fall, 1853-1945 (Modern War Studies Series) Edward J. Drea https://www.amazon.com/Japans-Imperial-Army-1853-1945-Studies/dp/0700616632

The Japanese Empire: Grand Strategy from the Meiji Restoration to the Pacific War S. C. M. Paine https://www.amazon.com/S-C-M-Paine/e/B001HCVOTG?ref=sr_ntt_srch_lnk_2&qid=1575464570&sr=1-2