Walgreens (WBA 3.69%) stock has been on a roll this year, with shares up more than 29% year-to-date . This is an impressive run for a company that's still recovering from its breakup and make-up with pharmacy benefits manager Express Scripts (ESRX). However, the rise of generics, international growth, and the aging population should also play to Walgreens' favor in the year ahead.

Top dividend stock
In addition to these catalysts, Walgreens is also one of the better dividend stocks to own. Walgreens stock pays an attractive quarterly dividend, and has done so without interruption for more than 80 years. Additionally, the company has earned its title as a dividend aristocrat by increasing its payout for 37 consecutive years. The stock's current dividend yield of 2.3% looks even better if you consider that over the last five years Walgreens stock has achieved a compound annual growth rate of nearly 24%.

The company's long history of payouts helped shareholders remain calm during a turbulent 2012. Most of the upset was related to the fact that Walgreens said goodbye to about $5 billion in annual sales when it lost Express Scripts' business. Because the drugstore chain would no longer fill prescriptions for patients in the Express Scripts network, it ultimately forced its customers into the arms of the competition.

Lessons learned
CVS Caremark
(CVS 1.49%) and Rite Aid (RAD 20.00%) benefited the most from Walgreen's fallout with Express Scripts. This is because at the time, both CVS and Rite Aid still accepted Express Scripts plans. The rival pharmacy retailers launched aggressive advertising campaigns that specifically targeted Walgreens customers whom held Express Scripts insurance .

It took Walgreens and Express Scripts nearly seven months to work out their differences -- costing Walgreens billions in lost sales. However, the two companies finally reached a new multiyear agreement during July of last year. Walgreens stock soared more than 10% last year on that news alone.

Around the same time, investors were also busy dissecting the company's acquisition of Alliance Boots. If you remember, Walgreens agreed to pay $6.7 billion in cash and stock for a 45% stake in the European drugstore chain.

Fast-forward to 2013
Today, Walgreens is proving that its 2012 purchase of Alliance Boots was less of a knee-jerk reaction to its Express Scripts woes, and more of a long-term play for international growth. Together with Boots, Walgreens inked a 10-year deal with pharmaceutical distributor AmerisourceBergen (COR 0.77%). As part of the agreement, AmerisourceBergen is giving Walgreens and Alliance Boots the option to buy a minority position in the company or as much as 7% of AmerisourceBergen's outstanding stock. Walgreens and Alliance Boots also received warrants exerciseable for a 16% equity position in AmerisourceBergen .

Both Walgreens stock and shares of AmerisourceBergen climbed higher last month when the partnership was announced. With AmerisourceBergen now handling Walgreen's branded and generic drug distribution, Walgreens should see increased efficiencies in its global pharmaceutical supply chain. Moreover, this was a smart move by Walgreens as it attempts to cut costs and strengthen its business abroad.