In John 18:37, Jesus says
For this cause came I into the world (kosmos) that I should bear witness unto the truth.
Just as he 'came into the world' so, on his leaving it, he sends others. So, where was he found ?
By the well in Samaria; right up in Decapolis (arguably a Gentile region) where he appears to have spoken to none except the SyroPhenician woman; by the rather questionable gathering at 'the sheep' where he spoke to none except the man crippled for thirty-eight years; in the temple; in the gate of Jericho.
He was found everywhere in Israel, right up to and (perhaps) a bit beyond its borders.
Kosmos is a very wide concept, as a glance at Liddel&Scott or Thayer or BDB or Strong will show. The EGNT (I don't know of an online version) sometimes translates it 'habitable world'. It could possibly bear the meaning of 'civilisation' or just 'the environment' depending on the context just as our own word 'world' has a very broad meaning, its usage depending on context.
He thought the world of her. His world extended no further than his garden gate. The world of art is passing strange. And so forth - a very broad concept.
To different people, the world means different things. Some people travel no further than a few miles from their home in their whole lives. The blind see nothing by sight - their 'world' is what they hear and touch.
To any individual, their 'world' is what is beyond their own domestic environs. In order to interact with other humans - other than very, very close family - I have to go out into the world.
Jesus is saying to his disciples that, in order to reach out to 'the whole creation' or to 'every creature' (I am not going to comment on the different translations), one must go out into the world, first, in order to interact with that which is created.
And I agree with you that it would involve interacting with human systems. Paul did so in his travels, taking ship on several occasions (and being shipwrecked). He walked around Athens and saw the various idols and saw the one 'to the unknown god'. And thus he preached to the Athenians.
Paul had a dream and crossed over to Macedonia where, by the riverside, he found a place where women prayed. And he spoke with them and Lydia invited he and his companions to her home, where she and her household were baptised.
Anywhere, everywhere. The whole world.
On my profile here, my website is mentioned. My website mentions Jesus Christ on the first page. And my website is advertised on Youtube and on Facebook.
Wherever God created, there is the name of Jesus Christ to be spoken.