1415-1420
The Hundred Years War
It took Henry 2 years to prepare before invading northern France in July 1415 and capturing Harfleur in September. Henry decided to March from Harfleur to his main base in Calais but found himself having to elude a numerically stronger French army before finding himself forced to select a defensive position or be destroyed in detain in the open.
The battle of Agincourt was fought on October 25th 1415, Henry's longbowmen ensured that very little hand to hand fighting took place. French Knights decimated their Genoese allies, armed with crossbows, in their eagerness to close with the English but were mown down in their droves by the English Longbow. The lessons of the Scottish wars had been successfully applied to European warfare.
Unable to take advantage of the battle because his communications with England were threatened by the Genoese fleet, Henry returned to England to build up his own fleet and gain control of the channel, driving off the Genoese in 1416.
Returning to France in 1417, with the channel now secure, Henry conquered Normandy, unlike Edward's use of the Chevauchee or raid in force, Henry occupied castles and strongpoints, creating a secure area of English control before pushing further south.
Also moving troops into Brittany, which had supported the Orléanists an English army under the Duke of Bedford defeated a combined Franco-Brittany army at Avranches forcing Duke John V, Henry's Uncle in law, to accept English Suzerainity and make common cause with Henry.
Later than expected, Albert V joined the war, capturing Paris in 1418 and massacring Orléanist leaders. He had been held up by a conflict with the Swiss Federation where, to free his hand in France, he had made concessions of territory.
English forces were besiegeing Rouen and its surrender was closely followed by the assassination of Albert by supporters of the Dauphin. In the confusion, Henry marched on and secured Paris for the alliance. Charles II, Duke of Lorraine and uncle of Albert, became regent for Albert's son, Frederick IV.
In 1420, with the Burgundian faction dominant in France, King Charles VI of France was forced to acknowledge Henry V as his heir, and as virtual ruler of most of France, signing the Treaty of Troyes and marrying Catherine of Valois to him to seal the deal.
The Dauphin, naturally did not accept the usurpation of his position and undertook negotiations with the Angevins of Maine and Provence to strengthen his cause. Unbeknownst to him, his plans had been revealed to Henry and his largest army was destroyed by a combined Anglo-Angevin force as it crossed the Loire.
Bohemia
England's ambitions lay further to the west but the influence of Theologian John Wycliffe, deemed a heretic and rejected in his own land, where the Lollard sect was suppressed, grew in Bohemia where the preaching of Jan Hus was widely heeded. Hus preached against the corruption of the Church and Papacy. The Church, in the midst of the Schism, both Popes selling indulgences to raise money to support their cause, did nothing to change the perceptions of a corrupt organisation in need of reform. Hus, denounced by the Church after explicitly quoting the heretic Wycliffe, won much support in Bohemia.
In 1414, Sigismund, King of the Romans, convened the Council of Constance to resolve the Schism and other religious controversies. Hus was offered safe-conduct to appear at the council but was imprisoned, tried and executed in 1415. A protest to the council from Bohemian nobles recieved only threats from Sigismund in return.
Disorder broke out in Bohemia, Catholic priests driven from their parishes, Bishops from their sees. From the start the movement had two factions, the Ultraquists [moderates] and the Taborites [extreme] but for the moment their aims were the same. Preparations were made to defend themselves against Sigismund. As if to ensure this need, Hussites attacked the town hall in Prague and threw town councilors, the burgomeister and representatives of the King from the windows into the street. The death of the King, soon after, may have been partly due to this, either way, Sigismund was heir apparent and intent on staking his claim.
Catholics were forced out over most of Bohemia, an attempt to re-instate Catholicism by force was defeated by a Taborite Hussite force under Zizka in early 1420, this act alone enabling the spread of Hussite influence to magnify even beyond the state borders.
Zizka instituted a strict military discipline and adopted a tactic not used before; the Wagenburg. In effect a mobile fortress defended with artillery and handguns.
The Wagenburg would be placed close to the enemy formation and artillery used to inflict great losses on enemy formation, provoking their attack. Defenders would then use firearms and crossbows against the [usually mounted] attackers who could not penetrate the "walls" of the wagenburg.
Sigismund was aided by the Pope in Rome who declared a crusade against the heretics. He arrived at Prague in June 1420 with an army from all over Europe, captured and garrisoned two castles but found it impossible to maintain a siege of Prague and so withdrew. The castles were promptly besieged by Hussite forces. When Sigismund tried to rekieve them he was decisively defeated, the castles capitulated and Bohemia fell firmly under Hussite control.
HRE
Part of Frisia was rent by a civil war [1413-1422] which invited outside interference, troops from the Habsburg lands arrived to make the peace and it was only the obvious aims of Albert V that enabled peace to be agreed.
Schleswig had been inherited by the Duke of Holstein in 1402 who proceeded to try to combine this Duchy with his own, alienating it from Denmark, part of the Kalmar Union. Denmark reacted in 1409 by seizing the Duchy, starting a prolonged war with Holstein. By 1417, Holstein, allied with the Victualling Brotherhood, a pirate society, had re-captured most of Schleswig and were pushing on.