On 21 May D'Aubigny and Sellat, the president of the parliament of Paris, arrived. Their object was to enlist James in the alliance made by the treaty of Cambrai, between the pope, the emperor, and France against Venice, and to consult as to the marriage of the daughter of Louis XII, whose hand was sought by Charles of Castile, and also by Francis de Valois, dauphin of Vienne. James advised the latter. He delayed entering into the treaty, and D'Aubigny's death, a month after his arrival, interrupted negotiations.
The death of Henry VII on 22 April 1509 altered for the worse the relations of the two kingdoms. James had now to deal with an ambitious brother-in-law as eager for the honours of war as himself. Though a formal embassy under Bishop Forman congratulated the new monarch, trifling disputes continued, and finally led to war. Quarrels on the border were incessant. Henry VIII detained, in spite of repeated demands, the jewels left to his sister by her father's will. He also aided the Duchess of Savoy against the Duke of Gueldres, kinsman and ally of James. In July 1511 Andrew Barton was defeated and slain. Both monarchs now began to prepare for war. The chief object of Henry was the invasion of France; that of James, of England.
James's relations with Louis XII had now become intimate. He had done his best to reconcile the French king with the pope and the emperor by twice sending the Duke of Albany, his uncle, and the Bishop of Moray to the pope to mediate in the quarrel, which threatened to involve all Europe, but without result. He also implored by more than one envoy the assistance of Denmark, but the king was engaged with his own internal troubles. When the pope formed the Holy league against France in October 1511 Scotland was France's only ally. James was energetically making ready for war during the whole of 1511, and completed the building, though not the outfit, of the Great Michael, which took a year and day to build, and carried, he boasted, as many cannon as the French king had ever brought to a siege. The preliminaries of his league with France were signed by him at Edinburgh on 6 March, and the treaty itself on 12 July 1512. By the former he engaged to make no treaty with England unless France was included; and by the latter none without the consent of France. Henry vainly sent Lord Dacre and West on 15 April to Edinburgh to prevent the completion of the league, but early next year James, with characteristic inconstancy, sent Lord Drummond to Henry to offer terms, which the English king refused. Leo X issued an excommunication or interdict against James in 1513, and immediately afterwards James heard that war was finally resolved on in the English parliament against both France and Scotland. Still, it was Henry's obvious policy to keep peace if possible with Scotland while he invaded France; and West was again in Edinburgh in March, when James promised to abstain from hostilities for the present, but would write no letter which would ‘lose the French king,’ though he ‘cared not to keep him’ if Henry would make an equal promise. West left it to the judgment of Henry whether ‘there was craft in the demeanour and answer’ of James. He reported that he saw on all sides building and equipping of ships at Leith and Newhaven, and the preparation of artillery and fortifications. When dismissed after some angry passages with James he carried with him a letter from Margaret, indignant at the detention of her jewels. The single request of Henry, which James granted, was the appointment of a commission to treat of the border grievances in June, but when it met it adjourned. No sooner had West left than De la Motte, the French ambassador to Scotland, arrived from France. He brought four ships with provisions, fourteen thousand gold crowns of the Sun, and, besides his master's letters, one from Anne of Brittany, sending a ring and appealing to James, as her knight, to succour the French kingdom and queen in their hour of need. The Bishop of Moray, James's envoy in France, to whom Louis had given the rich bishopric of Bourges, about the same time, sent a letter to James, assuring him that his honour was lost if he did not assist France. Despite the protest of Bishop Elphinstone and ‘the smaller but better part of the nobles,’ it was determined to declare war with England unless Henry refrained from attacking France. A letter, not so imperative in its terms as might have been expected, but asking Henry whether he would enter into the truce which Louis and Ferdinand of Aragon had agreed to for a year from 1 April, was despatched by Lord Drummond on 24 May (Ellis, Orig. Letters, i. 1, 76). On 30 June Henry, instead of entering into the truce, sailed for France and began active hostilities. James at once sent his fleet under Huntly and Arran to aid the French on 26 July, and on the same day despatched the Lyon king to Henry before Terouenne had arrived, with a letter which, after recounting all the Scottish grievances, ended by peremptorily requiring Henry to desist from the French war under the penalty of an alliance between James and the French. Henry gave a contemptuous refusal.