I'm just really curious how such a ridiculously obvious and simple design took so long to be invented and put to effective use in warfare. To my limited knowledge it peaked around the medieval age. I have no knowledge on the matter but common logic dictates that this is the equalent of spears being invented as late as the viking age or something. It just doesen't make sense to me, can someone explain it to me?
Similar bows were already in use by about 6,000 years ago (e.g., the Muldbjerg bow, from the early 4th millenium BC). The design might well be older, but wood doesn't survive very well from that long ago.
this is the equalent of spears being invented as late as the viking age or something
Since similar bows had already been around for thousands of years, a closer equivalent would be, although spears had been around for tens of thousands of years, why was the phalanx invented so late?
Clearly, more than just the invention of a high draw weight longbow is needed to have successful Hundred Years War English-style longbow armies. What are some of the ingredients?
Longbows.
Enough skilled archers so that you can field a force of thousands on the battlefield. One English solution was legislation: "ALL Sorts of Men under the Age of Forty Years shall have Bows and Arrows, and use Shooting; certain Persons excepted", &c. Unlawful Games "shall not be used." and similar laws.
Enough money to pay the archers, or some other system to entice/force them onto the battlefield in sufficient number.
An army that they can be successful in.
The right opponent.
The last two points are important. Longbow archers are not a superweapon that will win battles by themselves. They are part of an army that includes other types of soldiers. Notably, archers in battle need to be protected. English practice in the Hundred Years War was to use armoured infantry and field fortifications to protect the archers - when English forces were caught by the enemy without the opportunity to build field fortifications or deploy covering infantry, the English archers could be (and sometimes were) dispersed/killed by enemy mounted men-at-arms (e.g., the Battle of Patay, 1429, against the French, and Bannockburn, 1314, against the Scottish).
This needs to protect the archers also favours defensive battles. Ideally, one forms up the army in a defensive position, with archers protected by armoured infantry and/or field fortifications, and waits for the enemy to attack. In the Hundred Years War, the great "longbow victories" were such defensive battles. Had the French decided to not attack at Agincourt, the outcome may well have been very different - the English army could not wait in its defensive position indefinitely (or even for very long, due to dysentery and lack of food), and would have been much more vulnerable to attack on the march. In hindsight, the French were the right opponent due to their willingness to attack English defensive positions, and the Scottish were the right opponent due to their inferiority in cavalry (which made the battle less mobile, and helped protect the archers) and the relatively poor armour worn by the Scottish infantry (until the Battle of Flodden, 1513, when the Scottish infantry were sufficiently well-armoured to make English archery ineffective).
French efforts to emulate the English by fielding large forces of archers were not successful. They had the bow. What they lacked were (a) a system to ensure a large enough force of well-trained, motivated, high-morale archers on the battlefield, and (b) an army and enemy suited for battles in which longbowmen could play a key role.