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Although I understand the basic rules of the usages of articles, sometimes the usages of "the" can be quite confusing. I need a bit of help to help me get a deeper understanding about it. I really appreciate your help. Thanks.

Joe: Were the questions difficult?

Amanda: Not really. They were about Second World War/ the Second World War.

Which one is correct? I feel that it's fine with or without "the." The phrase Second World War is sometimes used with the, but it's not always used with the. If only one of the options is acceptable, I hope to know in what circumstances we should use the when we use the phrase Second World War.

In summer/ the summer, I went to China.

I think I should use the summer because it's a specific summer. Am I correct?

In summer/ the summer, I always go to the beach.

Both of them are correct? "The" is used here because that's how people use it even though it's not just a specific summer?

Some animals come out at night.

This one means every night?

I worked at the night. While I was working, I heard a strange noise.

This one means a specific night?

What about phrases of a famous organization like The White House, The Trump Organization, The United States?

How to decide whether they should go with the?

What about sea?

When should we use the with sea?

On a sunny day, we can use the/ a sea from our balcony.

Which one is correct?

I love living by a sea/ the sea.

Which one is correct?

Tourists often visit Tangkak, especially when weather/ the weather is nice in summer/ the summer.

I feel that both options are correct but I am not sure.

Must I say the weather because it is specifically about the weather at Tangkak?

This is a really long post. I am really thankful for your help. Thanks