If you access the Internet through a proxy, you will need to configure Maven to download dependencies through this proxy, following the Configuring a proxy instructions at the Maven page.

Basically, this consists of including the corresponding configuration in the .m2/settings.xml file:

<?xml version="1.0" encoding="UTF-8"?>

<settings xmlns="http://maven.apache.org/POM/4.0.0" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                        http://maven.apache.org/xsd/settings-1.0.0.xsd">

   ...

    <proxies>
        <proxy>
            <active>true</active>
            <protocol>http</protocol>
            <host>proxy.somewhere.com</host>
            <port>8080</port>
            <username>proxyuser</username>
            <password>somepassword</password>
            <nonProxyHosts>www.google.com|*.somewhere.com</nonProxyHosts>
        </proxy>
    </proxies>
</settings>