All wages and any other compensation for services performed in the United States are generally considered to be from sources in the United States. The place, where the personal services are performed, generally determines the source of the personal service income, regardless of where the contract was made, or the place of payment, or the residence of the payer.
Evergreen content, which is described as that SEO content which stays relevant for a long time after its initial publication, is a good way to generate income. Comprehensive research statistics and case studies, such as social media marketing trends for the last five years, and detailed how-to guides, such as a beginners guide to using Twitter for business, are always going to be sought after people who wouldn't mind paying small amounts for access to the information.
Others may define it more narrowly, but to me, PPC arbitrage basically involves setting up PPC ads (via Google AdWords or similar platform) and directing the traffic that results from ad clicks to a landing page or straight to an affiliate link (which many platforms don’t allow anymore).  The goal is obviously to earn more from the affiliate income than spent on the ad clicks.  You aren’t adding any value, but merely earning more from traffic than what it costs you to generate that traffic.
An obvious example is over exposure to bank stocks, which have been excellent investments for over a century.  Though a foundation of most portfolios, bank stocks do involve more risk at certain stages of the economic cycle than many realise.  Being less exposed to bank shares in the last few months could have preserved some capital.  So, a more diversified approach can help mitigate some of these risks.