What's the difference (if any) between "to go under" and "to go bankrupt" in the following sentences? 1- His company has gone under! 2- His company has gone bankrupt!
To go under means to deliberately shut down a business as a failure, especially due to lack of revenue.
To go bankrupt is a formal legal process where a business (or a person) declares that they are unable to pay back all of the debts that they owe. The courts may then require them to sell off certain assets and use the proceeds to pay back some of that debt, while other debts may be forgiven and never paid back (which is why some corporate bonds trade at lower than face value - because of the risk that bankruptcy may erase the guarantee).
These two events are often correlated - a business might begin the process of going under by declaring bankruptcy, but they are not the same thing and do not always both happen at the same time.
For example, a business might go under because the owner decides that it's no longer profitable, but they may have enough assets (either in the business or personally) to pay down their debts without needing to formally declare bankruptcy.
Likewise, the process of going bankrupt and dealing with bankruptcy court does not necessarily mean that the business ends - sometimes it may continue operating, perhaps by offering some of its creditors a share of the ownership of the business, for example, and emerge from bankruptcy without going under.
Here is a list of eight famous companies that declared bankruptcy, but ended up profitable in the long run. That is, they did not go under.
"Gone under" is a metaphorical description of business failure, comparing it to drowning by going under the surface of the water. "Go bankrupt" is a possible legal recourse of a business that fails.
As pointed out in the comments and the other answer, I was wrong to say the terms mean the same. "Gone under" means that the business failed completely, one way or another. "Bankrupt" means to take legal action (of various kinds, described as chapter 11, chapter 13, or whatever) to discharge debts or dispose of assets of a company that has failed.
Thanks for the corrections.