As a result of the concept of nuclear deterrence during the Cold War, both the United States and the Soviet Union were unwilling to build dangerous, destructive weapons, which would have encouraged war.
both the United States and the Soviet Union were willing to build weapons that were increasingly dangerous to stop the other side from attacking.
both the United States and the Soviet Union signed treaties to deter the development and testing of nuclear weapons.
both the United States and the Soviet Union agreed to work together to develop and test nuclear weapons to prevent future wars.

bless you your highness

the industrial development of cities in the ruhr area in the nineteenth century is described. the research was based on english and german language sources. several factors that shaped growth and paths of the cities were categorized and analyzed. they are locations, resources, traditions, entrepreneurs, and technological developments. locations and resources were the most important among them; other factors may be regarded as consequences from locations and resources. among the cities, bochum, essen, gelsenkirchen, and dortmund had the richest resources and most favorable locations in the transportation network and grew to be the largest cities in the ruhr area near the end of the nineteenth century. riverside location was also a favorable factor for the development, as shown in the development of duisburg on the confluence of rhine and ruhr. resource distribution can explain the rise of textile industry, metallurgical industry, and coal and iron industries, and the northward progression of the mining industry. tradition was an important factor for cities such as krefeld, barmen, elberfeld, solingen, and remscheid, which experienced development based on their traditions through the nineteenth century. various entrepreneurs exerted influences within and beyond the local level over the ruhr area. technological development stimulated the northward progression of the mining industry and the deep connection between the coal and the iron industries.

answer:   migrations were important in the neolithic period. "two major migrations passing through southeastern europe were confirmed by the means of archaeo-genetic studies."

the first migration was the early neolithic period -- 6,000 before common era (bce) -- when the first farmers, from anatolia -- asia minor -- spread through europe. the second migration occurred during the early bronze age (3,000-2,500 bce) when the so-called "steppe population," from the eurasian steppe, replaced much of northern europe's previous population.

the first farmers of northern and western europe passed through southeastern europe with limited hunter-gatherer genetic admixture, which occurs when two or more previously isolated populations begin interbreeding. however, some groups that remained mixed extensively -- without the male-biased, hunter-gatherer admixture that prevailed later in the north and west, according to latest discoveries. southeastern europe continued to be a nexus between east and west, with intermittent genetic contact with the steppe people up to 2,000 years before the migrations that replaced much of northern europe's population.

"in some places, hunter-gatherers and incoming farmers seem to have mixed very quickly," says iain mathieson, a geneticist at the university of pennsylvania, who was first author of the paper. "but, mostly, the two groups remained isolated, at least for the first few hundred years. these hunter-gatherers had been living there for thousands of years, and it must have been quite a shock to have these new people show up -- with a completely different lifestyle and appearance."