it's also illegal to send cash like, that
Not in the USA.
they can confiscate those money if they caught you to do so
Not in the USA. Who is "they" and why would they "confiscate" it?
i get those from my country, if the amount surpass a certain level, your cash can be confiscated because they go against the money laundering thing
they need to know from where those money coem from, "they" is fiscal agent/fiscal police
Excellent point! Cash over a certain amount is almost always considered "suspicious" (in the US). What are the limits? Probably buried in the USPS website somewhere.