A strategic alliance is very different from networking. And the implications are vastly different. A strategic alliance is a mutually beneficial relationship with another business where you both speak to the same target market.
In other words, you are building a relationship with someone who is hearing what your prospects are saying about their issues (the ones you can solve) and vice versa. Moreover, they can't be built with just anyone in that industry. The key is to find those people who you click with. People who you can actually build a long term relationship with to the benefit of both of you.
Networking is great - and random. You build relationships with all kinds of people and at some point in time, they MAY refer you to a client, friend, or family member. I am a big fan of networking. It is where you find your strategic alliances.
With networking, you want to build relationships with different kinds of people - getting to know them as well as you can and helping them whether or not they are ever able to help you directly. Indirectly, it will pay off time and again.
Strategic alliances are targeted relationships with specific people in specific industries (maybe even your own) who feel the same way. The arrow goes both ways here and you are both able to not only help each other, but help your clients and prospects with each other.