I do (although there may be some outlying communities not in contact with the rest of humanity.) Most of the world is linked through trade of goods and services as well as the flow of information (newspapers, radio, TV, and the Internet.)
shareNot if we speak with nuance. Ancient civilizations were often linked by trade routes too. Western Civilization dominates the world, and other civilizations and uncivilized regions have Westernized to varying degrees, but in places important cultural differences remain. There are still fundamentally non-Western aspects to the Islamic world, China, and much of Africa and other Third World regions.
But the scientific society responsible for modern transportation and communication is Western and broadly encompasses the earth, so in some narrow senses it makes sense to speak of humanity as currently having one civilization.