The Internet business looks a bit like Europe before WWI. It’s a tense landscape rife with rumor, arms races, border skirmishes, secret pacts, and colossal ambition.

A spate of recent headlines tells the story. eBay seeks a common front with Microsoft and Amazon against Google. Amazon drops Google technology from the Alexa search engine. Microsoft debates absorbing Yahoo. Google complains that Microsoft’s new browser is anticompetitive. MSN debuts its adCenter. On Monday, Yahoo unveiled an interactive search advertising engine (see Yahoo Rebuilds Ad Engine).

If there is a common theme, it’s that Google is a threat and it needs to be contained.

On Wednesday, when Google hosts its annual media day in San Francisco, the company will have scores of technology and business reporters ready to broadcast whatever new weapons it may train on its gathering competitors. Google is not going to easily relinquish its share of an Internet advertising market that reached $12.5 billion in 2005.

Some of the speculation has pointed to a new health vertical from the Mountain View, California company, which remained tight-lipped on Monday. “Health has been an area of interest at Google for some time. We have been doing a variety of research in the health area, including how to improve the quality of health-related search results. We have nothing new to announce at this time,” said Google spokeswoman Jennifer Hakes.

Dan Schatt, an analyst at the consultant firm Celent, said he will be looking for more products along the lines of the calendar Google released in April.

As Microsoft bolsters its search offering with an eye on Google’s core business, Google has been assembling an array of online applications that pose a danger to the hegemony of Microsoft Office. In March, it bought Writely, an online word processor.

Google could also threaten eBay, said Mr. Schatt, by combining Google Base, which allows people to post items for sale, with a financial transaction tool along the lines of eBay’s PayPal, which streamlines online commerce for small merchants. “Google could start moving down that path as well,” said Mr. Schatt.

Nothing’s Forever

There are many directions for Google to take, but whatever announcements Google makes, it will not hold on to its dominant position forever, said Rick Summer, an analyst with Morningstar.

Mr. Summer said that competitive search products from Ask, Yahoo, and MSN will encroach on Google’s share of the search market, which stood at 42 percent in March, according to comScore Networks.

Mr. Summer also believes Google will lose its outsized share of the online advertising market as competitors cut more favorable deals with advertisers, and search technology continues to evolve.

Pointing to the software package known as Google Pack, introduced at a trade show in Las Vegas in January, Mr. Summer noted that past Google products announced with fanfare have not been smash hits.