天下大乱

the whole country is in chaos

天下太平

peace rules over the land

天下第一

the best in the world

天下无双

unequalled in the world

我们的朋友遍天下

our friends are all over the world

走遍天下找不到

search the whole world without finding it

这样的人是天下少有的。

This isn't the kind of person you meet every day.

得了天下

obtain rulership

今天是劳动人民的天下。

These days the workers rule.

当时敌后的广大地区都是人民的天下。

At that time, the vast area behind enemy lines was ruled by the people.