Invasion without war

maybe you r right Of way with him

Else

A very bad bug

It only triggers a war when they get to a "dot". Walking the road until there doesn't start the war, yet. I'd be very worried that it will soon, though...

If I try and do it I get a warning that war will be declared..

The message says says it MAY be declared. It isn't declared quite yet.

War is not actually declared until either damage is done or a province is captured. You can enter or even land troops in neutral nations without actually going to war.

IF I see a neighboring country troops entering my nation without them declaring war I do not wait for them to reach their objective point without moving my own troops into position to defend and I make sure I am not the aggressor to trigger a surprise attack. (for the Global Popularity) If the province they are advancing thru is not a key resource province I may even allow them to capture it and then cut them off. If North Argentina is entering more than one of your provinces you can be sure they are planning a surprise attack, there is no other reason for a neighbor's troops to be entering your lands.

It's pretty annoying how you eat up popularity penalties for engaging an intruding and most likely hostile unit. Firing a barrage on an advancing 2 dozen unit strong army who's already 30km deep into your territory shouldn't be treated as an unprovoked aggression.