(1)What weere the most important political, social, and economic developments among the major European nations between the 1860's and World War I? (2)Were they comparable to those taking place in Canada and the United States?
If we are thinking teleologically toward World War I, then politically, the most important developments, in hindsight, were the development of alliance systems in Europe. This did not involve the United States as such, but certainly created a war that the US would struggle to avoid. Economically, the rapid industrialization of most western countries would have to be the most important development. It was important precisely because of its social ramifications. It led to massive social unrest in western countries, as working classes became increasingly proletarianized, and in many European countries, most conspicuously Germany and France, radicalized. Many historians have argued that these pressures from below, unleashed by industrialization, helped contribute to the outbreak of the First World War.
Between 1860 and 1900, one of the greatest social developments in Europe (England specifically) was the introduction of Darwin's theory of the mutability of species through natural selection of the characteristics most fitted to the species' environment. We know this as Darwin's Theory of Evolution. On the Origin of Species was published in 1859 and its effect rocked religious and academic circles throughout Europe and in American and Canada all the way through to 1900--and beyond. Two specifics are that, (1) in America, universities fired professors for promoting Darwin's ideas and, (2) in England, Herbert Spenser's social philosophy, popularly called Social Darwinism, applied Darwin's ideas to social structure by suggesting that certain races had become superior, an idea that fitted imperialism exactly.
Imperialism as a political development and nationalism as a social one were common threads throughout the major European empires at that time. The industrialization mentioned above was the prime factor driving the need for resources and thus, further colonization. This led, in part, to the nationalist movements that justified taking colonies and subjugating other peoples.
I agree with #4 that we can also stress colonialism, although clearly industrialisation would be the most important. The time period you specify featured the European powers in a mad rush to scrabble for whatever colonial territories they could get their hands on. The US and Canada of course did not have this experience in the same way, as they were geographically removed from any location that they could reasonably lay claim to, such as the vast continent of Africa.
Curiously, Italy, Germany, and the United States were all going through a difficult process of becoming Nation States in the 1860's, fighting either political or actual military wars of unification. The development of new and expansion of existing Nation States was rapid during this time; chief among the factors occuring was the colonization of the world -- all the major powers were in fierce competition to establish, retain, or expand their colonies. That was one of the reasons for conflict between colonies, culminating in conflict between the Mother Nations in World War I.
I agree that industrialism was the most important development in its effects on all these countries. It's possible to argue that colonialism was also very important, although in a sense Canada was itself still a colony. The European powers, in particular, were competing with one another to establish and/or maintain colonies.
The common thread was indeed industrialization. Germany and the United States both became heavy industrial countries. However many immigrated from Germany to the United States at that time, because there were more opportunities.
Industrialization was the biggest social and economic development going on in Europe during these years. It was definitely going on in the United States and in Canada as well. A development that was going on in Europe but not so much in the US was the rise of nationalism. This was the era in which, for example, Germany and Italy each became united countries encompassing most people of their respective "nations."
Social: women were finally taking a stand for what they believed in and believed that they should be treated equally to men. ex. getting the right to vote or getting a job