article from the Catholic Encyclopedia describes his papacy, he had great impact on the Catholic Church in England and left an important legacy for the universal Catholic Church with his many (12!) encyclicals on the Rosary, his ground-breaking social encyclical, Rerum Novarum, and other Catholic devotions, like the Prayer to St. Michael the Archangel:
Saint Michael the Archangel,
defend us in battle;
be our protection against the wickedness and snares of the devil.
May God rebuke him, we humbly pray:
and do thou, O Prince of the heavenly host,
by the power of God,
thrust into hell Satan and all the evil spirits
who prowl about the world seeking the ruin of souls.
Sancte Michael Archangele,
defende nos in proelio;
contra nequitiam et insidias diaboli esto praesidium.
Imperet illi Deus, supplices deprecamur:
tuque, Princeps militiae Caelestis,
satanam aliosque spiritus malignos,
qui ad perditionem animarum pervagantur in mundo,
divina virtute in infernum detrude.
As to his influence on the British Empire and Ireland, the Catholic Encyclopedia article notes:
Among the acts of Leo XIII that affected in a particular way the English-speaking world may be mentioned: for England, the elevation of John Henry Newman to the cardinalate (1879), the "Romanos Pontifices" of 1881 concerning the relations of the hierarchy and the regular clergy, the beatification (1886) of fifty English martyrs, the celebration of the thirteenth centenary of St. Gregory the Great, Apostle of England (1891), the Encyclicals "Ad Anglos" of 1895, on the return to Catholic unity, and the "Apostolicæ Curæ" of 1896, on the non-validity of the Anglican orders. He restored the Scotch hierarchy in 1878, and in 1898 addressed to the Scotch a very touching letter. In English India Pope Leo established the hierarchy in 1886, and regulated there long-standing conflicts with the Portugese authorities. In 1903 King Edward VII paid him a visit at the Vatican. The Irish Church experienced his pastoral solicitude on many occasions. His letter to Archbishop McCabe of Dublin (1881), the elevation of the same prelate to the cardinalate in 1882, the calling of the Irish bishops to Rome in 1885, the decree of the Holy Office (13 April, 1888) on the plan of campaign and boycotting, and the subsequent Encyclical of 24 June, 1888, to the Irish hierarchy represent in part his fatherly concern for the Irish people, however diverse the feelings they aroused at the height of the land agitation.
When Pope Leo XIII made Father John Henry Newman a Cardinal Deacon of the Church, he knew it was a controversial move--he called Newman "my cardinal" and said, "My cardinal! it was not easy, it was not easy. They said he was too liberal, but I had determined to honour the Church in honouring Newman. I always had a cult for him. I am proud that I was able to honour such a man."
May Pope Leo XIII, Gioacchino Vincenzo Raffaele Luigi, rest in the peace of Christ. Image credit from wikipedia commons.