Wanegffelen sees him as the royal most responsible for the massacre, which involved the targeted killing of many Huguenot leaders. Henry III's reign as King of France, like those of his elder brothers Francis and Charles, would see France in constant turmoil over religion. Henry continued to take an active role in the Wars of Religion, and in 1572/1573 led the siege of La Rochelle, a massive military assault on the Huguenot-held city. At the end of May 1573, Henry learned that the Polish szlachta had elected him King of Poland (a country with a large Protestant minority at the time) and political considerations forced him to negotiate an end to the siege. Negotiators reached an agreement on 24 June 1573, and Catholic troops ended the siege on 6 July 1573. King of Poland and Grand Duke of Lithuania (1573–1575) Following the death of the Polish ruler Sigismund II Augustus on 7 July 1572, Jean de Monluc was sent as the French envoy to Poland to negotiate the election of Henry to the Polish throne in exchange for military support against Russia, diplomatic assistance in dealing with the Ottoman Empire, and financial subsidies. On 16 May 1573, Polish nobles chose Henry as the first elected monarch of the Polish–Lithuanian Commonwealth. The Lithuanian nobles boycotted this election, however, and it was left to the Lithuanian ducal council to confirm his election. The commonwealth elected Henry, rather than Habsburg candidates, partly in order to be more agreeable to the Ottoman Empire (a traditional ally of France through the Franco-Ottoman alliance) and strengthen a Polish-Ottoman alliance that was in effect. A Polish delegation went to La Rochelle to meet with Henry, who was leading the Siege of La Rochelle. Henry left the siege following their visit. In Paris, on 10 September, the Polish delegation asked Henry to take an oath, at Notre Dame Cathedral, to "respect traditional Polish liberties and the law on religious freedom that had been passed during the interregnum". As a condition of his election, he was compelled to sign the pacta conventa and the Henrician Articles, pledging religious tolerance in the Polish–Lithuanian Commonwealth. Henry chafed at the restrictions on monarchic power under the Polish-Lithuanian political system of "Golden Liberty". The Polish-Lithuanian parliament had been urged by Anna Jagiellon, the sister of the recently deceased king Sigismund II Augustus, to elect him based on the understanding that Henry would wed