Have or has?

[Xenon32]

I have a doubt about to use "have" or "has". Why in the first sentence is used the singular third person and it doesn't used in the second sentence?
"In the last hundred years, traveling has become much easier and very comfortable."
"Things have changed a great deal in the last hundred and fifty years."

[mykwyner]

Traveling, in this case is what we call a gerund. It is a verb (to travel) acting like a noun, a singular noun.
Things is an ordinary plural noun.

I, we, you, they, those, these, (every person except third person singular) have...

he, she, it, that, who, has