(~s)
1.
If there is an ~ into a country, enemy soldiers suddenly enter it. (FORMAL)
...armed ~s into border areas by rebel forces.
N-COUNT: oft N into n
2.
If someone or something enters an area where you would not expect them to be, or where they have not been found before, you can call this an ~, especially when you disapprove of their presence. (FORMAL)
...her disastrous ~ into the property market.
N-COUNT: oft N of n