I would like to know what difference is there between überfallen and attackieren. Is it correct to think that überfallen could be a person who attacks another one, while attackieren could be an army or a state attacking another one? In which contexts is one better than the other one? Can they be synonym?
Überfall could be translated to raid or hold-up. It can be a kind of break-in. In most cases an Überfall is done to steal something. It can be used as Banküberfall which means bank hold-up. If someone threatens a person (or uses violence) and want something valuable, that could also be considered a Überfall.
This is a very similar word to Raub, which also means theft with use of violence. Sometimes these words get mixed up to Raubüberfall. In most cases a Raubüberfall indicates more violence than an Überfall. In most cases überfallen is something very fast. Therefore it could also be used to say, that an attack was very fast and surprising. But that's rather unusual.
Attackieren simply means to attack. This word does not include that a attack is made because of profit. It could also be done because of revenge or fun or some other reason. Not only states, but also persons can attack each other. The goal of this kind of attack is to harm somebody/something.
Attackieren puts emphasis on violence. You can attack someone verbally or physically.
Überfallen has a few meanings with subtle differences. All of them have in common that it's about a sudden, unexpected "attack" (don't know a better term here).
First, there's robbery. Robbery is possible without violence. Second, you suddenly confront someone with something. That does (usually) not include any form of violence. And third, there's a military attack, which most like include violence.
Synonym to some extend I think
Both would work in a military context I think.
In everyday conversations attackieren would be one person attacking/insulting another person. With words or physically.
überfallen always is a physical thing. A raid, a military engagement that was not to be expected at that point in time or in that form.
In personal conflicts Attackieren is used when it is an attack on someones life or at least physical integrity whereas überfallen is used to describe an action to "gather something" - steal personal property/money - so it is not against a person but against the belongings.