Overnight

[NewHope]

I don't get
"These countries did not get to be the way they are overnight. They don't change overnight."

Context:
'You can build a house in three years," he said. "You can build a house in three months. But rebuilding systems is a different thing.

"These countries did not get to be the way they are overnight. They don't change overnight."

[Casiopea]

I don't get
"These countries did not get to be the way they are overnight. They don't change overnight."

Context:
'You can build a house in three years," he said. "You can build a house in three months. But rebuilding systems is a different thing.

"These countries did not get to be the way they are overnight. They don't change overnight."

Things take time. 'overnight' means, quickly. For example, if a tsunami destroys your house, you can't rebuild it in a day, let alone that night (i.e., overnight).

[NewHope]

What do "they" refer to in "the way they are overnight"?

[Francois]

These countries.

FRC

[Marylin]

What do "they" refer to in "the way they are overnight"?

As Casiopea and Francois explained...they refers to the countries and overnight means "right away". Same with the saying: Rome wasn't built ina day. Rebuilding of countries from disasters takes time and therefore it's not an "overnight thing", it's not a snap - it's a process.