This sort of list by its very nature can lead to overly simplistic and monolithic explanations of history and not every general claim will apply to every country or every decade.

Given those caveats, changes in gender roles have been quite dramatic in developed countries. In these countries, women can now hold property, get divorced, and have the right to equal treatment in the workforce and education. Although women have not caught up fully with male salaries, in most advanced economies, they match male rates of education and have increasingly close rates of labor force participation.

Two other gender and familial structures are gradually changing as well. The twentieth century marked a shift from extended to nuclear families as a basic household unit, with there also being a dramatic rise in single person and single parent households. This has changed the urban and suburban landscapes of many places. The growing acceptance of gay relationships and growth of gay marriage has also meant a change in family structures.

Changes in the economy and in transportation technology have fundamentally reshaped the human geography of the developed world. A reduction in the number of people involved in food production has led to increased urbanization and depopulation of rural areas and small towns while the ubiquity of the automobile has led to the growth of suburbs and urban sprawl.

Many people, including some financial experts, trace our current state of consumer-mania, for lack of a better term, to the period after World War II.  After servicemen and women began returning home, Americans were ready to have some fun, and many found "fun" in the purchase of suburban, cookie-cutter type homes, and lots of new appliances and services. . .and the ability to purchase them on credit.  John Lennon once said, "If everyone demanded peace instead of another television set, then there'd be peace."  

1. Women's place in the job market as well as new-found power in corporate and political settings.
2. The advent of the Internet and the many electronic devices that are associated with it.
3. The fall of the Soviet Union, the rise of China, and the U.S.'s self-proclaimed position of global policeman.

I'll stretch my entries by combining severall possible individual items into the overall category of "Technological Developments" - computers, both business and personal; electronic communications of all sorts; satellite-supported connections making the world so much smaller, and on and on.

Number 2 - Global community - by which I mean the increasing extent to which people can and do move from place to place, country to country. The changes in cultures that are being brought about in response to increasing numbers of immigrants into a given society are (hopefully, in my opinion) going to enrich all of our lives.

Number 3 - The planned obsolescence, conspicuous consumption mindset that is endangering our supply of natural resources and our environment.

1. The development of electronic communications--particularly the cell phone. This has changed how everyone communicates and has influenced the "Arab Spring" that we are currently witnessing. Countries can't the dissemination of information like they used to.

2. The commercial development of personal computers. Just about everyone can have what only rich corporations used to be able to afford.

3. The collapse of the Soviet Union. This changed international relations for everyone.

The rise of China will probably make the top three in the next decade or so.

Honorable Mention: The Drug War, The decline of American education, the near collapse of the Euro and the European Community.

1.  The end of colonial empires.  This was trending before the end of WWII, but the war definitely ended it.

2.  The Cold War.  While it isn't still going on, it dominated the landscape of the western world for 50 years after the end of WWII, and the spending that resulted crippled the USSR and left the United States the lone super power.

3.  The Global Political Community.  Nato was and the UN is very powerful and will continue to grow more powerful in the coming years.

You could go a lot of ways with this.  I'll go with:

• Globalization which has brought about the rise of countries like Japan and now China.
• The change in the status of women.  Women play a much different role in Western societies than they did in 1945.
• The decrease in religiosity in most Western countries.  Europe has become much less religious, leading to changes in what holds their societies together.