International cooperations support developments in many fields, and today’s big issues cannot be solved by a single country.

Technological advancements of recent years are the fruits of globalization.

For example, leading companies in the field of information technology are multinational.

They hire their employees from many countries, produce and sell them all around the world.

What is "them" here? The way you wrote it, it sounds like the companies are producing and selling employees.

Because of that, they, ands well as technologies related tof their fields, are developing at an astonishingly fast pace.

Environmental issues are taken as a serious problem among all countriesll over the world.

If countries take responsibility only for damages ofwithin its own regionborders, how canould we tackle with the problem of melting polar ice sheets or that of pouring acid rains?

Today, international organizations such as uthe United nNations, COP21, and so on contribute to environmental protection.

Political issues are also in need of an international approach.

or: "Political issues also need to be approached/tackled/dealt with internationally."

Pressing political problems including environmental ones are so huge and complicated that a single country cannot solve them.

For example, reducing strategic weapons, especially ones that includes nuclear warheads, needs international cooperation.

Treaties on limiting weapons are the only way to improve the situation, and the existing ones awere made ofrom global effort.

The more technologies develop and populations grows, the more huge and complex the society becomes.