The term “second industrial revolution” is commonly used by historians to refer to a period of rapid economic development, mainly, but not exclusively, limited to the western world of the late 19th and early 20th centuries. Details will wary with time and place, but in general the period is characterised by large scale mechanisation of production, both in secondary industries and the primary sector.

Domestic agricultural development and growing access to imports freed up rural populations for work in the new industries, leading to rapid urbanisation, which in turn drove the growth of service industries. These developments both fuelled and were made possible by "revolutions" in finance and communications, facilitating the flow of goods, capital and services between producers and consumers on a global scale.

Historians commonly use period labels for easy reference, rather hard delineation. When historians talk about “the second industrial revolution” they are thus talking about a large number of concurrent processes, rather than a fixed number of years. The start and end points of these “revolutions” will depend entirely on your focus and frame of reference. The liberalisation of Danish financial activity and foreign trade began in earnest with the abolishment of the Sound Dues and adoption of the Trade Act of 1857, leading us to identify the latter half of the 1850s as the beginning of the period in question. Meanwhile the mechanisation and subsequent exponential growth of Danish agriculture is spurred largely by the establishment of large agricultural cooperatives in the 1880s, leading agricultural historians to focus on that decade as the start of the industrial revolution. The adoption of a gold standard as a basis for international currency transaction, facilitating the large scale movement of capital which in turn fuelled industrial and infrastructure investment in the western periphery, is only beginning to be realised from the late 1870s onwards, leading students of this aspect of the economic transformation to identify the 1870s or the 1880s as the beginning of the industrial revolution.

There is thus no hard start date for the second industrial revolution, just as there isn’t for most such periodisations. Your defined period of study will depend entirely on your chosen focus or which question you want answered.