Nouns have always been written in small letters in English. They used to be small in German, too. The following says that they started using capitals in nouns in German in the 16th century: http://www3.germanistik.uni-halle.de/weber/sc...

Laut wiki:
The convention of capitalizing all nouns was previously used in English, but ended circa 1800. In America, the shift in capitalization is recorded in several noteworthy documents. The end (but not the beginning) of the Declaration of Independence (1776) and all of the Constitution (1787) show nearly all nouns capitalized, the Bill of Rights (1789) capitalizes a few common nouns but not most of them, and the Thirteenth Constitutional Amendment (1865) only capitalizes proper nouns.

Oh, actually, the above link says that the process of nouns being capitalised in German began in about 1670 and went on until 1850.

Wikipedia also says: It was also done in 18th century English (as with Gulliver's Travels and most of the original 1787 United States Constitution). http://en.wikipedia.org/wiki/Capitalization#Nouns

and "Old English, for example, was rarely written with even proper nouns capitalised; whereas Modern English of the 18th century had frequently all nouns capitalised" http://en.wikipedia.org/wiki/Latin_alphabet

This book also mentions it being used for a short time in the 18th century: http://books.google.co.uk/books?id=79tSVMWuTN...

It was a passing fad - when you see an English Text with Capitalised Nouns you know it came from that particular period.

Minuskel und Majuskel waren die zwei im Mittelalter verbreitetsten Schreibweisen. Vereinfacht gesagt, war Minuskel alles klein und Majuskel alles in Grossbuchstaben. Daraus hat sich dann ueber lange Zeit hinweg eingebuergert, dass wichtige Woerter mindestens mit Majuskel anfingen und alles andere drumherum in Minuskel stand. Man denke an die wunderschoenen Initialen in mittelalterlichen Handschriften.

Wichtige Woerter waren in den meisten Faellen Substantive.

Im Deutschen kam die Großschreibung meinen Informationen nach in der ersten Hälfte des 16. Jh. auf.
Luthers Bibelübersetzung, zitiert aus Sekundärliteratur (leider sind die Bildchen in google so klein):

1523
Und Gott sprach, last uns menschen machen, eyn bild das uns gleych sey, die da hirschen ubir die fisch ym meer, und uber die vogel unter dem hymel und uber das viech, und uber die gnatzen erde, und uber alles gewurm das auff erden kreucht, Und Got schuff den menschen yhm zum bild, zum bild Gottis schuff er yhn, und er schuff sie eyn menlin und frewlin.

1545
UND Gott sprach, Lasst uns Menschen machen, ein Bild, das uns gleich sey, Die da herrschen uber die Fisch im Meer, und uber die vogel unter dem Himel, und uber das Vieh, und uber die gantzen Erde, und uber alles Gewuerm das auff Erden kreucht.
UND Gott schuff den Menschen Im zum Bilde, zum Bilde Gottes schuff er jn, Und schuff sie ein Menlin und Frewlin.

"Eingeführt" is not the right word, as you recognize by your Anführungszeichen. The best word to use would be "Wann hat sich das eingebürgert?" and the answer would be gradually over the period between 1750 and 1820. But if you go back to before about 1660, you will find that nouns were not normally capitalized, although usage was pretty arbitrary.

As for German, it is interesting to note that books printed in the early 20th century in Roman type rather than Fraktur also tended not to capitalize nouns. Hitler abolished Fraktur for general purposes in 1940, possibly the best thing he ever did. Pity he didn't abolish capitalization of nouns at the same time.

Zu AGB # 5

dass wichtige Woerter mindestens mit Majuskel anfingen

In vielen älteren Bibeln werden die Gottesnamen mit zwei Großbuchstaben geschrieben: GOtt, HErr ...

As far as I remember Henry Fielding (Tom Jones etc.) and other contemporanean writers wrote most of the nouns with a capital letter and the texts are also printed this way in the well-known classic editions for students.