Answer:
A. barbed wire
Explanation:
Barbed wire was a revolution in the cattle industry. Before the barbed wire people would grow big hedges with thorns or build wooden fences and that was expensive. Barbed wire fence would be made with wire and only poles to keep the wire in place and that cut the cost tremendously and allowed farmers to mark their land while keeping cattle.
So basically to explore places like you want to travel and stuff you need money for the flight or whatever.
I'm guessing you are talking about WWI.
Thus, we were "officially neutral", but we gave arms to both sides. However, we gave more to Britain and didn't stop their blockade. This made Germany mad and pushed them to start Uboating our ships. So, we retaliated by eventually not economically financing Germany, before we got into the war.
:<span>The United States was officially neutral but its trade policies mostly helped Britain and France.</span>