In 1949, I discovered the magazine, 'Astounding Science Fiction'. Over the next thirty years or so, this magazine has given me much pleasant reading. One of the authors, Randall Garrett, wrote about an alternative history in which magic blossomed rather than science. Magic or, to give it its proper name, Thaumaturgy has existed almost as long as man himself. In its modern form, it can trace its roots back to the Norman invasion of England. It is even rumored that the arrow that felled King Harold was directed by magic. Garrett's hero, Lord Darcy is a detective in this milieu. These stories are in the way of being a tribute to Lord Darcy and to Randall Garrett.
Imagine a world in which King Richard Coeur de Lion (the Lion-hearted) didn't die suppressing a revolt in France, but instead returned to England a much chastened king. There he ruled wisely and founded a dynasty. This dynasty still rules England and France today, as well as much of Europe and large swathes of the rest of the world. America was divided into two Dominions: New England the Northern half and New France, the Southern half of the continent. On the far side of the world were the dominions of New Holland and New Zealand.
This is a much more stable world than the readers' own. The Church has escaped the division of the Reformation, although variations in the forms of worship are tolerated in New England. The colonies' claims in 1774 for representation in the Westminster Parliament were met with sympathy. This resulted in the recognition of the local legislatures and raising the status of 'The Colonies of New England' to that of Dominions. Subsequently, most of the remaining colonies achieved Dominion status as well.
New England comprises the whole Northern half of the continent from the polar ice cap to the land the readers know as Mexico. The southern half of this continent, including Mechicoe, is known as New France. During the last century, the 1900's, the comparatively light population along the Atlantic coast, expanded explosively to the rest of the country. This was largely due to the discovery of gold and the spread of the railways.
The work of William Wilberforce in abolishing slavery in Europe, was echoed in the Dominion of New England by the work of Governor-General Lincoln. He skillfully avoided martial confrontation by emphasizing the financial gains to be made by abolition. He suffered by losing his life to the one man he couldn't convince.
The world is largely at peace. The Angevin (Anglo-French) Empire is vying with the Kingdom of Poland and it's satellites in a state of cold-war with occasional hot spots. Both Empire and Kingdom regard each other's way of life as wrong as did the Americans and the Soviets did in the readers' world.
In addition to the local police officers, there are two Dominion-wide law-enforcement agencies. The Royal New England Mounted Police cover the northern part of New England while the southern part is served by the New England Bureau of Investigation.
With the rise of magic as a logical discipline, science has been slow to develop. Science has generally reached the stage that it had in the early 1800s, As in the readers' universe. Steam power has been well exploited. Steam trains offer an alternative form of transport to the horse-drawn kind. Diesel engines are, at the moment, laboratory toys!
Electricity is almost unknown in this milieu. Magic has produced substitutes and analogues of many devices that are familiar to the reader. One notable feature which is missing is the telegraph. Hence, the survival of the Pony Express is assured.
A flashlight, with magical parts, is "a fantastic device, a secret of His Majesty's Government." Voice messages can be exchanged by a magical device called the "teleson", but the principles by which it operates are not well understood, and as yet its range is limited. It is impossible to communicate across oceans. The teleson corresponds to our telephone, but suffers, from the lack of trans-oceanic range and the need to renew its spells at regular intervals.